Lawfare Archive: Orin Kerr on the Digital Fourth Amendment

I'm Marissa Wong, in Turnet Lawfare.

With an episode from the Lawfare Archives for May 9, 2026. On April 27, the Supreme Court heard oral argument in "Chantry vs. the United States." The case centers on a Fourth Amendment Olegal Search Challenge to the government's use of Geofence Warms. For today's archive, I chosen episode from January 9th, 2025, in which Jack Goldsmith

sat down with Oren Care to discuss Care's new book on how the Fourth Amendment has adapted or remained stagnant in the digital age. The pair discuss the history of the Fourth Amendment, how its protections are complicated by the advent of the digital world, and how courts have interpreted the Fourth Amendment and light of new technology.

[MUSIC] If the lawfare podcast on Jack Goldsmith from Harvard Law School, with Oren Care, a professor at

“Stanford Law School, that's what equilibrium adjustment ends up being.”

It's sort of carrying out that instinct to try to find some middle ground in a world where the technology is constantly coming along and saying, "Oh, you have that Olegal rule?" Well, guess what, that legal rule that was balanced in the old world is now unbalanced in the new world, and it either dramatically expands government power or dramatically cuts back on government power, and now it stinks, what are you going to do?

Today we're talking about his new book, the Digital Fourth Amendment, privacy and policing in our online world. I think it's fair to say that you're the world's expert in this field, but you tell an interesting story, an interesting anecdote in your introduction about how it almost

didn't come to be about your first job in the Justice Department, and the kind of difficulties

you faced in entering the field. Yeah, well, first of all, thanks, Jack very much for having me on. The story of how I started in Fourth Amendment Law and Computer Crime and Digital Evidences. I was hired by Mistake, showed up the first day of my new job at the Justice Department. I was so excited, I was going to be a cybercrime prosecutor, it was the fall of 1998, early

internet boom, and I showed up at the office and they said, "So where are you going?" And I said, "I thought I'm going here," and they were like, "Oh, we were afraid of that." Yeah, it turned out they filled out the wrong form, and they wanted to interview me, but instead they hired me, and they were stuck with me, and they made absolutely clear. They did not want to hire me, and I ended up working on a lot of legal issues about Computer

Crime because there was basically nothing else I could do. I was right out of a clerkship, I was 20, whatever, seven years old, and I knew nothing, and so they gave me all these legal projects because they figured, "Well, you know, at least the kid can do law," and I ended up just absolutely loving these amazing legal issues that were just beginning to happen, and I kind of built a career on that since.

And you said you worked on that they gave you a task that nobody else wanted, working on a manual for use by federal and state prosecutors on the law of digital evidence investigations,

“and in a way, that's what this book is about.”

Right? Yeah, that's exactly right. This is kind of, you know, many, many years later, quarter century later, this is the legal

issues that I first saw, and it was an amazing experience because I started off looking

at these fourth amendment issues and some statutory questions, and they said, "Right, I'm manual on how to investigate Computer Crime cases," and I started looking at these old cases and thought, "Well, this doesn't really fit modern technology. This doesn't really quite work. How are courts going to figure this out?"

And I started seeing those legal issues, and I knew I wanted, I was interested in becoming a law professor at some point, and I switched directions. I think originally I'd wanted to go into administrative law, was my love of legal love in law school. I thought that was going to be awesome, and instead, I said, I, you know, I should start

doing this, because no one else is doing this, and this looks like it's going to be big over time.

“So that's kind of switched directions, and that's what I ended up working on.”

Well, you've had quite a career working on it. This is a great book. The book is kind of in a way what you just described. It's about how the old fourth amendment doesn't really fit with new digital technology and what's to be done about it, how to work that out.

Can we just start at the beginning and just remind listeners what the fourth amendment is, what it says, what it purports to do? Yeah. So the fourth amendment prohibition on unreasonable searches and seizures, enacted as part of the original amendments to the Constitution and ratified in 1791.

At the time, there weren't police as we know them today. The authority was mostly about limiting the scope of warrants, court orders, that the

And that had to be limited in certain ways.

That's what the 18th century focus was.

“And then you start getting police in the 19th century.”

This whole idea of law enforcement sort of a full-time police officer gathering evidence, making arrests in the like. And so the Supreme Court started really in the 20th century. It starts looking at this 1791 language and saying, we kind of need to use that craft. The primary limits on policing.

So the modern role of the fourth amendment is it's what limits arrests. It's what limits breaking into someone's house. It's what limits stops and frists. It's sort of it's the main constitutional limit on policing in the United States today. And as it was deployed in most of the 20th century, as you just described, it had to do with

physical spaces. Can you explain the extent to which the fourth amendment kind of rested on an assumption about physicality? Yeah. So in a world of physicality, think back to the 18th century or 19th century, fourth amendment

was really about physical space and what could be done in physical space. And the rules are very physically based, you know, government needs a search warrant to break into someone's house. Government does not need a search warrant to watch someone in public. That's sort of a very physical conception in figuring out how broadly a search can go,

how, you know, what's the scope of a search? The search unit might be like a house, one physical house. The government can get a warrant to search a house where evidence can't get a warrant to search a city block for evidence. That's not a particular warrant.

So just the rules of search and seizure naturally took on a physical aspect in a world where searches were unaided by technology, just kind of physical searches by officers, just naturally that evolved in the rules. And then, and I'm just kind of marching through the early part of the book to set up the hard problems.

And then the digital world descends on us. And so the whole book is about how to understand the fourth amendment and the doctrines that were designed and conceptualized in this physical world and how to apply them to the digital world, which is a whole, had the whole different set of conceptual assumptions. So just gives an overview of why the digital world is different and then we'll unpack

how to think about it. So the rules of search and seizure, the rule of sort of where can the government go to collect

evidence and whatever it can collect is always going to be dependent on what's the technology

of where the evidence is. And so think about how a modern investigation might unfold where the key evidence in a case is information, you know, a text message somebody said, for example, or something

“like that, or evidence of web surfing, where's the evidence going to be located?”

Well, it could be on a physical digital device that has a ton of other information on it and it's just stored as a digital record of past behavior, something which didn't exist as much in the physical world. You could have letters, of course, but most people wouldn't sort of put their every move into a letter in the 18th century.

And then online, think of so much of what we do, including recording this podcast, it's mediated by a digital network. It's something that's going to be stored by a server. It's a digital file somewhere, and so the government has to figure out who is behind the keyboard, where is the file located, who might have possession of that file?

The evidence has dramatically changed from the old physical world, where it's just kind of officer walking through physical space, looking at things, needing a warrant to break into a physical space. Now we're looking at just sort of data all around the world, and how can the government

“get it and the techniques for getting it and the rules for getting it?”

It's just that old physical assumption just doesn't, we can think about what's the modern version of that world, but we can't just simply apply the old rules to it, because we end up with in a lot of ways, kind of a fourth amendment, free zone. If the rules, think of just sort of how you translate the legal rule into the technology. If the rule is the government needs a warrant to break into a house.

The government can get all of its evidence without breaking into a house, well then all of a sudden the fourth amendment doesn't mean very much anymore, it's just the government can do all the surveillance it used to without physical invasion, and you say, well, that's okay, or do you instead embark on this task of kind of figuring out what's the modern day equivalent of a physical invasion in order to restore the role of the legal protection

and the new technological world?

And your theory for answering that question, the most important idea in the book, as far

as I'm concerned, a hugely important idea, is called equilibrium adjustment, and that's

what it means, can it maybe use an example from one of the Supreme Court cases?

“Yeah, so the basic idea is to maintain the role of the fourth amendment over time not the rule”

when those two diverge, and the idea is really it started off as just a description of what the Supreme Court has done with past technologies ranging from the telephone to cars, to lots of other examples. The fourth amendment is kind of innately about technological change because where the evidence

is is always going to be contingent on what the technology is used to carry that evidence

and to store that evidence. So the Supreme Court in the past, I looked back at old Supreme Court cases, this is going back to an article I wrote about a decade ago, it's sort of how does the Supreme Court respond to new technology when this happens? And I began to see there's actually a consistent method that Supreme Court has, which is

as the technology changes and shifts how much power the government has to collect evidence. The court seems to respond to technology by shifting the rule to restore the prior level of government power. And so in an example of this, let me actually give an example that I start the book with is cars in the 1920s, the role of technology, there was a dramatic shift in technology that

had huge implications for the fourth amendment, which was suddenly everyone was driving a car and they were carrying evidence in cars. And the problem that the court's had was that if you kept that old legal rule of having

a warrant requirement, then suddenly that you could never actually investigate a car

crime because people just drive away before the warrant was obtained. And the Supreme Court in 1925 case called Carol versus United States says, well, we're basically we're dropping the warrant requirement for cars, what's known as the automobile exception to the United States. We still have it 100 years later.

And the idea is, well, just practically speaking, you can't investigate a case involving a car, an evidence in a car in less you shift the rule to a no warrant rule to just probable cause responded to the technology, kind of trying to balance, sort of, basically the idea is to say, listen, technology is shifted the ground so much under the prior legal rule that we need to adjust the rule to restore the equilibrium and maintain the role

of the fourth amendment over time. And so you see this, in some cases, the Supreme Court loosens rules where the technology is made at harder to investigate. And in other cases, the Supreme Court strengthens legal rules or adds legal juice to the rule to increase legal protection in response to technological change.

And you see this across the Supreme Court's cases, cars, telephone, sense enhancing devices,

“GPS, all these cases, I think you can really see a consistent method in the Supreme Court's”

cases of grappling with technological change by trying to maintain the role of the fourth amendment, not the legal rule and I give that the fancy title equilibrium adjustment because the thought is it's trying to, the court is adjusting the rules to restore that prior equilibrium. So, I have to say, once you see the theory, you see it in every one of these cases, it's

amazing how, no matter what the doctrinal commitments of the justices and their different

ways of looking at what equilibrium adjustment means, but it's just on the surface of the cases, especially the digital cases as we'll get to, but even the old cases, it's quite remarkable. Yeah. They all do it.

Yeah. They all do it. As you say, independently of theoretical commitment, if you're an originalist, a non-originalist, living constitutionalist, they all have the same deeply, deeply felt need to do this. And there is one interesting example, Justice Black, turns out, was not in favor of this method.

“Everybody else, cross the board, though, they all do this and have, but I think what makes”

it really interesting is, you know, this goes back a long, long ways, goes back to the very early fourth amendment cases and it's been consistent throughout. So I just want to press you a little bit on what's being adjusted to what? So the fourth amendment doctrine is changing. The court is changing the doctrine of the fourth amendment rules in order to, and I'm just

not sure which one of these things are all of these things it is. Is it to preserve the purpose of the rule? Is it to preserve the role that the fourth amendment was playing? And I don't know quite what that means. Is it to, you also said it was to kind of maintain the government's level of power.

We don't want to give the government too much power to surveil, but we don't want to give them no power because law enforcement needs. Just being adjusted to what? Concretely, and maybe I don't know, cats is that an example that we can use to illustrate this?

Yeah, so there are lots of, lots of great examples and cats is one of them.

I think what's being adjusted is maintaining the role of the fourth amendment.

I mean, think, think really, go back to real basics here. Imagine a world with no limits whatsoever on the police. The police can break into anyone's house at any time. They can arrest anyone at any time, absolute total police power, zero privacy rules. We would all look at that and say, that's just absolutely horrible.

That is a police state. That is dystopia. Why? Well, too much government power is the power to abuse the rules, abuse the authority to the privacy rights of someone's house, arrest someone.

It's all of these bad things that happen if they're zero legal limits. So we can think about why that is and come up with our economic and answer for costs here and cost there. Really, what's going on?

Just a police state would be bad, that's the intuitive way of thinking about it.

And we can look on the other side, too. Imagine a world where the police had no authority to investigate cases at all. They're not allowed to break into someone's house at all. They're not allowed to arrest anyone at all. They just have zero ability to do any of these things.

We also look at that and say, well, that's also a dystopia. Someone commits a murder. And they say, I'm going to kill someone again tomorrow. And the police say, gosh, we wish we could stop that person, but we can't. We have no authority to arrest them.

We'll just let it happen. And that seems also really bad.

“And so I think you've got sort of just the nature of policing is there these two extremes”

that are horrible.

And there's something I'm not going to call it a sweet spot.

It's maybe it's just sort of better than the rest. Somewhere in the middle ground, enough power to enforce the law, but not too much power to abuse the law. There's some sort of instinct we have in people with different, you know, a Bill Rankwist is going to end up with one sense of what's perfect and a Brennan is going to end up

with another sense of what's perfect with there. They're each going to have some sense of somewhere in between those two radical extremes. There's a, there's a better world. And I think that intuition is what's driving a lot of this. And it's kind of, you know, you can think of it as an optimization of some kind of overall

public benefit and often forcement power, but not so much harm to civil liberties as kind of legal externalities on a lot of policing. You can't think of it that way, but it's also just like, listen, those two extremes are horrible. Those are dystopian, like that's, that's like bad movies and stuff we'd want to avoid.

So avoiding the horrible is really what's going on here.

“And that's why I think justices from all sorts of different ideological commitments, they”

can all realize when a rule is leading to outrageous results. And they will think of it that way. They would just be like, no, no, no, no, that's terrible. We don't want that. What we don't want, we don't want to world where either there are no limits at all on

policing, or there's just no ability to police. And so they're naturally going to try to kind of look for some middle ground between those two. Enough limits on the police, not too much limits on the police are going to have that instinct. And that's, that's what Equilibrium adjustment ends up being.

It's sort of carrying out that instinct to try to find some middle ground in a world where the technology is constantly coming along and saying, oh, you have that illegal rule, well, guess what, that legal rule that was balanced in the old world is now unbalanced in the new world. And it either dramatically expands government power or dramatically cuts back on government

power. And now it stinks, what are you going to do? And so they're all going to kind of look for that middle ground. They're all going to engage in this, this method, usually instinctively, they're not going to be thinking about it as, you know, they're not, obviously, like academics, they're

justices, practical sort of, they're going to look for that middle ground and they're going to keep doing this across all these different technologies. OK, but there's, there's lots of room between those two polls. And a lot of the argument in the book is about how to find the sweet spot as you put it.

“Can you use cats as an example to, and do you think, I think you think cats was a proper”

equilibrium adjustment to explain why the old physical world rules weren't working in a light of new technology and why that was the right adjustment? Great. Yeah. So in cats, the FBI is investigating someone who's a bookie.

He's using a public pay phone to place bets for his clients and the FBI tapes a microphone to the top of the public pay phone booth and records half of the call, the cats' side of the call, whenever he's placing the bets. And the prior rule had been a search occurs when there's physical intrusion into a protected area.

And so the ninth circuit below says, well, there's no physical intrusion into a protected area here. This is merely a microphone taped to the top of a phone booth and so there's no intrusion into anything and it's just a public pay phone, it's not like someone's house either.

And the Supreme Court says, well, physical intrusion doesn't matter anymore. What really matters is was it kind of a privacy invasion. And I think of it as being, they're basically asking, was it the modern day equivalent of a physical intrusion? They're looking at the facts and they say, well, we're now in a world where people are having

their most private conversations on phones, and in 1967, pay phones were a crucial way

people did that. So listening in on someone's pay phone calls like an incredible privacy invasion. And so they adjust exactly what rule they adopt is a mystery. The opinion is kind of a hard opinion to parse, but they're expanding Fourth Amendment protections in the rule in order to maintain the role of the Fourth Amendment.

You can't invade privacy like that, like listening in on someone's phone call, because technology that microphone had expanded government power under the prior legal rule. Let's move more deeply into the digital.

“And let's talk about the carpenter case, which I think is the most important case in the”

digital world in the Fourth Amendment, I'm not sure if you agree with that, but I just think this case is so important if you could just maybe give us the background in terms of the third party doctrine, explain why the third party doctrine seemed problematic to some in carpenter, how the court resolved it. And I don't think you talk about this much in the book, but I don't think, because you

had to work with the doctrine in the book, but I think originally in your scholarship, you weren't thrilled with carpenter, I'm not sure if that's right. But why don't you just tell us about carpenter? Yeah. So, so carpenter is the Supreme Court decision from 2018 saying that there are Fourth Amendment

rights in cell site location records at least at scale. And so cell site location information, those are records that your cell phone provider is automatically creating about which cell sites your phone was connected to when it was on. So whenever you turn on your cell phone, you get five bars or four bars or whatever it is.

That's actually the strength of a connection between your phone and local towers, local cell sites that are connecting your call.

“And the idea is whenever you're connected to the network, you need to really connect”

to the network. And your phone is actually sort of seeking nearby sites in order to connect. And what that means is that the phone company is creating records of where you are by virtue of creating records of which cell site you were connected to, and cell providers use this for network reasons, not for law enforcement reasons.

They want to know where people are they might say, hey, we need to add a new site over here because it turns out a lot of people are using our cell phone network over here and maybe less over there. And they use this for network reasons. Well, it creates effectively tracking information about where people were in the past.

If you assume people are next to their phones, which most people are, that cell site location information is going to effectively allow the government to roughly track where someone has, and in the, in the carpenter case, it was a guy involved in a string of robberies, ironically, of cell phones, he was going into radio shacks of the like and stealing cell phones with a group of co-conspirators.

“And the government helps to show this crime and part through cell site records, the records”

at the time were not very precise. So it's within a half mile to a mile and a half of the location, but still that's pretty useful. The government shows, hey, look, whenever this store was robbed, all of these phones were in the area of the robbery, and you know, the next day, it was 50 miles away and they were

all over there. And the next day was 100 miles there and they were all over there and so the government relies on this. And the Supreme Court says, we used to have a rule or we do have a rule traditionally

that if you disclose information to a third party, this is the so-called third party doctrine,

you don't have fourth amendment rights in what you disclose. So I'm talking to you, Jack, on this podcast. If I tell you I robbed a bank yesterday, the government can go to you and say, did Kurd say anything about robbing a bank, and you say, yeah, he told me he robbed a bank. And the thought is basically, when I disclose to you, I've given up my rights in what

I tell you, that information is now yours. It's no longer mine. And that has been applied in a couple of different network settings, most importantly, a case called Smith vs. Maryland involving numbers, dialed of a telephone, when I place a phone call, think in 1980 technology, I dial the number, and I'm telling the phone company,

hey, can you connect me to this number? And that's information I'm basically telling the operator in a pre-computer world, please connect my call. That's records to them and they can disclose that. In that world, the content of the calls protected under the Fourth Amendment, but the government

can go to the phone company and say, what number did Kurdile and get that information, because that's a record to the phone company.

And the government argued in Carpenter, well, this third party doctrine applies, because

after all, this is basically information disclosed to the network for network purposes,

And that meant that there was no Fourth Amendment protection in these cell site records. And the Supreme Court's answer is pure equilibrium adjustment. They say, we have to say these records are protected, because there has been a seismic shift in technological change, these records are unlike anything that is existed before. And if we don't say this is protected under the Fourth Amendment, then suddenly the government

has this massive windfall of power that's been granted to them. They can engage in cell site tracking of everyone for years, and we can't live in that world. And the way the Chief Justice Roberts frames it is like the Fourth Amendment, he actually sort of uses this balancing framework.

Fourth Amendment is trying to limit the power of the government, but not too much. And this shift has occurred. And he's very much using this equilibrium adjustment type language.

And so the end result is kind of an exception to the third party doctrine, which everyone's

still trying to figure out. We don't quite know what carpenter means seven years later. But it's that and Riley versus California from 2014 are the two digital Fourth Amendment

“cases where I think the court is taking these instincts and trying to craft a new kind of”

digital, digital specific Fourth Amendment. And a lot of the book is basically saying, okay, these are the two examples of the Supreme Court has gotten to already. What's the picture going to be or should be 20 years now, 50 years from now, 100 years from now?

And in a lot of ways, the inspiration for me is I think back to the 1920s when the Supreme Court decides the Carol case saying there's this automobile exception.

So many could have written an amazing book in the 1920s, playing out how the automobile was

changing Fourth Amendment rules and saying, here are all the rules. There's got to be a kind of car specific automobile specific Fourth Amendment. And that is, in fact, what we have, I'm teaching Fourth Amendment law today. And very much, it's this sort of technologically specific world of here are the car cases, here are the home cases.

And we just, we're going to need to add to that here are the computer cases. And so we can, we can already now kind of see what this world should be. And the point of the book is to play that out and start looking at a bunch of the big questions and see what this world that we're aiming towards should look like and will look like and think through it comprehensively now rather than just look at individual cases as they come

up. So you accept and try to theorize about, come up with a three-part test for the carpenter rule in the book. But do you think it got the equilibrium adjustment right? It does seem to me like at one level the fact that our phones are spewing off all this information all of the time massively, massively, and powers the government compared to the earlier baseline.

But I think you think it's more complicated than that in terms of equilibrium adjustment. So can you tell us whether you think that that was the time in the place and the right way to adjust for the amendment to deal with cell towers?

“Yeah, so a key, key question behind this approach is you have to identify when has there been”

one of these seismic shifts, when has there been a moment where those old rules just really don't work anymore. And they've either given the government this huge windfall or they've, they've done the opposite. They've dramatically lessened the government power to enforce the law. And this is, I disagreed with carpenter, I wrote an amicus brief in the case saying that we're

just not in an adjustment point yet. And the reason why is that in the technology of 2018 when the case was being decided, the cell site records were not that precise, as I mentioned, it was within a half mile to a mile and a half, and once you, once you say these cases are different, it's actually pretty hard to figure out exactly what are the cases that fall within that rule, sort of.

You're creating an exception to a very clear rule, what's the exception and that can be done, but it's actually quite hard to figure out exactly where the carve out is here. And I basically said, this is not enough of the shift. And what this Supreme Court said was, well, this case happens to involve half mile to a mile and a half kind of like not really precise surveillance, but we are confident that the technology

has already shifted to being GPS like precision that it's, you know, going to be within 10 feet or 20 feet, and that this is tracking that's extremely precise. And we, we think the technology is already there given the five-year-old record, and we think it's, that's where we are going to be, and that's, so the court takes that as the technological assumption that the nature of this tracking is extremely precise.

And then proceeds from there, they say, well, if we have this extremely precise tracking,

“what does that mean and they come up with this rule?”

And if you accept the factual assumption that I think, I like carpenter, I think it's

right, the problem is that even today, that technological assumption has not actually played

And from what I can tell, cell sites surveillance is still this kind of one mile kind of in the neighborhood in the town, not on which city street or which room kind of stuff.

“So I think the Supreme Court is maybe overly ambitious in thinking through what the technological”

shift would be. So love the method, but think, yeah, probably the facts didn't support it in that one case. And it makes me wonder what the proper unit of analysis is, and figuring out equilibrium

adjustment later in that chapter, you talk about some of the open questions about the third

party doctrine in the digital world now that people are, it's, of course, trying to sort out with regard to carpenter, and just to list those quickly, log in addresses, IP addresses that we visit every time we, you know, click on something on the web, ride sharing records when we take uvers and lifts, we throw off data about where we're going, geo-fensing and reverse keywords.

And these are just five examples. I assume they're 10 or 15 or 20 more. And I guess so my question is, should the court in doing carpenter have been thinking about all of those cases as well, indeciding, went and how to do the equilibrium adjustment? What is the unit of analysis?

It seems like a very hard problem to me because on the one hand, boy, thinking through the implications of carpenter and all these other contexts is super hard. And you do a good job of it in the book, but on the other hand, if we don't adjust in some sense, then the government is massively empowered. So how do you think about that set of questions?

So I take the method in carpenter, and I look through the opinion and think through the concepts of how we could look at what Justin could apply.

“I basically say there's this three part tests that I think emerges from this that fits”

the overall theme of the doctrine and fits what the court was doing in carpenter. And I play that out, how does that apply to logging IP addresses and how does that apply to web surfing? And in some cases, I think should be lead to this adjustment and should be protected. Some shouldn't, some I'm genuinely just like, I'm not sure how that one should play.

How to couple, I think are just, you could go either way. And so I don't think the Supreme Court should have thought through those questions. And the, the carpenter opinion is very expressly narrow in a sense. The court has this section where they say like, we are not changing all these rules. We are not talking about this.

We are just dealing with these facts. And that, you know, that makes sense. There's narrow in that sense and let the lower courts work through all these variations. And lower courts have started to work through these variations. One of the things that I think, the court maybe was not thinking about in carpenter was that it

actually turns out that because of, I think it's mostly because of limits on the scope of the exclusionary rule, it's actually quite hard to get a merits ruling on a novel for the amendment issue these days. There's so many ways out that lower courts have to avoid ruling on the merits. They'll say, well, this is a close call.

The good faith exception to the exclusionary rule applies. We are not going to decide what the legal rule is.

And so you just never get answers to a lot of incredibly important questions.

And what happened after carpenter is, if you look back at sort of how the Fourth Amendment law Fifth Amendment law developed in the 1950s, '60s, there were just an incredible number of cases that resolved a lot of doctrine pretty quickly. What we've had instead is carpenter in 2018. And then relative radio silence, Supreme Court has not touched any of this stuff.

And lower courts because of the good faith exception have actually not addressed a lot of these things. So, there are a lot of really hard issues to tease out. And I offer some answers in the book, a direction of courts might go. But the surprising thing actually is that we have not had this rush of cases seven years

later to fill in what the answers might be under carpenter. But in general, of course, at least, have said, well, this is narrow where at least

not going to establish lots of new rules here, although the court can never control the

impact of its breath. And it's said that many times in cases that turn out to have large implications. But can you just make sure everybody understands explain briefly what the good faith exception is and why that takes care of a lot of the cases? The good faith exception to the exclusionary rule is basically the rule that when there

is a Fourth Amendment violation suppression is not automatic, sort of exclusion of the evidence is not automatic. And the Supreme Court, in a series of cases, starting the 1980s, expanded this exception.

“And really, I think the key cases, 2011, Davis versus United States, where the Supreme”

Court says there's no suppression remedy if the government relied on then existing appellate precedent. And what does that mean? And if you are a criminal defendant or a lawyer for a criminal defendant, and the rule was against you and you want to argue that the rule should be changed, you can make that

argument. But even if you win the US Supreme Court, they say, congratulations, carpenter. You have, you know, the we're changing the rule, you get no benefit from that because the court

precedent.

What that means is it, first of all, if you're a lower court judge, you don't have to

reach the merits of these novel issues. You don't have to reach the merits of these, let's change the law kind of arguments. Even if you do, you don't have to give no one gets relief, actually, carpenter doesn't get relief. No one actually, you rightly doesn't get relief.

No one actually gets out of jail.

“It all becomes, I think, kind of advisory opinions that can be issued.”

And the unfortunately, the implication of this is that a lot of criminal defense attorneys will not raise novel forth Amendment arguments because they know it's not going to go anywhere. Even if they win, their client is not helped. And so it's just not on the mind of a lot of defenseless.

It reminds me of qualified immunity and the, where the court will give immunity unless the law that was violated was clearly established, which the court goes off on that grounds

law courts often do means the doctrine just can't develop because they never get to the actual

merits. But it wasn't clearly established enough. And this sounds similar to me, it sounds like a real structural hurdle to need a doctrinal development. Yeah, and it's particularly painful for me because I have argued one U.S. Supreme Court case

and it was Davis and I lost. Oh, wow. So I didn't know that. Yeah, so I see it sighted like every day and it just is like a, it's just painful every day to see that.

So you lost the case and it keeps the court from taking other cases in your field pretty much. Yeah. Okay. Let's move on.

So I just want to talk about a couple of other digital issues. One that I'm particularly interested in is Mosaic Theory. Can you explain what that is? How it relates to equilibrium adjustment. Yeah.

So this is an idea that maybe fourth amendment protection should be about scale that as soon as the government conducts a certain amount of surveillance, you get a search and it goes back to the DC circuits opinion on the way to the U.S. Supreme Court in the Jones case. And that was the case involving 28 days of GPS tracking of a car. And the DC circuits said basically, well, they put the GPS device on the guy's car.

They start tracking him. That's not a search. But at some point by 28 days, a search has occurred because that tracking lets the government learn so much information about someone. You can really, if you know where someone goes over 28 days, wow, you've learned a lot about

them. It's sort of the equivalent that you might learn about them by going into their house. And therefore, a search has at some point occurred. And this gets to the U.S. Supreme Court and there's no majority view for this theory, but there are some concurring opinions that endorse it.

And it's still in play today with lower courts dividing over whether there is an aggregation sort of limit on non searches that become searches or to flip it if something that's a search becomes a non search when it's done at a small scale. And so lower courts are just hopelessly divided on this question. But I take that on because that's another really important question of, if you accept

“that there's a at scale kind of special rule, you have to figure out, okay, well, what's”

the scale, and it leads to these endless line drawing questions about sort of how much is enough. How do the police ever know what they're doing is a search or not a search? Because they might not know when they, you know, press the button on the tool, how much information and what information is it going to collect. They might not know.

And so it might be that there's a search depending on what the answer to that is and they don't know that ahead of time. And I come down pretty hard in arguing that this mosaic theory is just completely unworkable. There's just no lines that can really be consistently coherently drawn. And I think that the instinct, I think, is great.

The instinct is basically saying technology allows the government to gather more information. That's what we're worried about. We're worried about the government having this extra power through technology like GPS tracking over time.

The problem is that in in equilibrium adjusting, if an adjustment is needed, you need to do

so with a bright line rule that says, you know, this whole method has now a search rather than you can do a little bit, you just can't do a lot.

“It's that kind of middle ground that I think is unworkable.”

And I use to go through some examples of course, trying to draw these lines that I think have just been a total failure in saying why courts should reject this method. So let me press you on the bright line rule requirement, which you and I both like bright line rules. But the counter argument is that just because you can't come up with a bright line rule,

doesn't mean you shouldn't try to lay down a principle and work it out over a set of cases, especially in a world where the government, you talk, I think it's in this context that you talk about artificial intelligence, maybe it was buying data. But especially when there are tools where the government can potentially, first of all,

Second of all, the government has tools that can increasingly harvest this data.

“I think to learn more and more powerful things about us, really intimate things about”

us. Just based on just a metadata, a critic would say the demand for rules is really putting a thumb on the scale for the government because during the period in which this government power is growing asymmetrically and we can't find clear rules, the government's just going to be a winner and shouldn't we do something like maybe what cats did and not being

very clear or what carpenter did and not being very clear and just indicated shift of direction. So what's wrong with that argument? So first let me take on the idea that rejecting the Bosaic theory is like a pro government view and a lot of circumstances, it's a pro individual view, you know, explain that.

So where this plays out, you know, can the government use cell site location information

to track someone for a few hours? Can they ping all the places that a particular phone was connected for, you know, a day or how many phones were connected, a tower dump, they call it as sort of how many phones were connected to that cell tower or the maybe they think there are two robberies, they want to know if they were connected.

So they'll say, let's get all the phones that were near the two towers at the times and near where those robberies occurred.

“And so if you're a mosaic theory fan, you say, is that a search?”

Well, I don't know, maybe maybe not. Let's see what the government learned and my answer would be, no, no, that's a search. They're all searches. Whenever you get cell site location information, categorically, that's a search. And so that's a situation where I end up much more civil libertarian than the mosaic

theory adherence. And I think what happened is, if I could just speculate, you know, the mosaic theory becomes its introduced in Jones as a way of taking non-searches and making them searches. Now it's taking searches and making them non-searches, it's sort of the sort of political or ideological vials is going to shift or flip back and forth depending on the context.

And I think the challenge is just, the Supreme Court of Massachusetts Supreme Judicial Court has been the leading proponent of this theory and what they have done in a series of cases is they look at the facts and then they look at the information that was gathered and then they say, looking at it now, we say there was a search. Or looking at it now, we say there wasn't a search.

Now interestingly, the Massachusetts Supreme Judicial Court, if I understand their procedure, they actually can do a pre-trial appeal to the state Supreme Court so that allows them effectively to rule on motion to suppress before trial. Federal courts don't have that. And so what happened in a federal court is you, the criminal defense attorney, file your

motion to suppress and then you can tell your client, listen, in five years we'll get a ruling on whether there was a search here. But that's the, this constitution should be noble to the police, not to justices looking in an appellate record years later.

“And so I think we're talking just about enough clarity to have some idea what the constitution”

allows the government to do is really the, it's not that high of a bar.

Okay, let's talk in terms of examples, finally about buying data.

I think the idea is that there's lots, you know, we give data away, individuals give data away, companies do things with that data, including selling that data that we give away. And the government can buy that data. They can purchase it and they often do purchase it in the commercial marketplace as I understand

it. And all outside of the scope of the Fourth Amendment, I think most statutory rules as well. So the question is, is the, is the, is the mammoth production of data by individuals, the mammoth collection organization analysis of that data by companies. And then the mammoth selling to the government, which can use the data in theory without

even worrying about the Fourth Amendment, is this an equilibrium adjustment situation? And my answer is maybe some day not now, most, it's funny, most of the book ends up being pretty civil libertarian, most of the time, arguing for adding Fourth Amendment juice to the system. And this is one area where I say, no, I don't think the case has been made.

In part because the idea that this is a seismic shift has not been established yet, there's a lot of concerns that this is going to be a seismic shift. But the evidence, at least so far of the government buying Fourth Amendment protected data as kind of a way around carpenters, a way around the Fourth Amendment rules, it's actually really, really hard to find examples of this happening.

And there's also responses by internet providers, by the providers themselves, by the companies, to try to thwart this from happening. And so what seems to be going on, we're so early in the, this particular dynamic to tell, but what seems to be happening is when there's a story about the government trying to buy

And part of that response is the internet provider saying, we're going to block this.

So you have Apple adding privacy protections, not allowing apps to do certain things. You have Google ending their kind of holding of location records that people have opted into for geofence warrants. It turns out the privacy picture is not as bad as some people think. At least from the public record.

That may change. The end of the year or 20 years we look back on this and we're like, you know, hey, you said it wasn't so bad that it was sure is so bad now, but at least right now we haven't that factual predicate that kind of like end of the world, oh, not end of the world. But like, wow, dramatic shift in government power, a lot of fears of it happening.

I haven't seen the evidence of it happening. You are unusual or at least on one end of the spectrum amongst legal scholars and your

scholarship has cited a lot by judges.

And you just said you followed me because briefs and you already the case in this prem court. And you talked in the introduction about and you thanked. You talked about having dialogue with judges about your scholarship. And this is all great in my opinion and extraordinary.

“Can you talk about a couple of things one, what are those conversations like?”

Are these like arguing about doctrine and two? How do you think about the relationship between your scholarship and what judges do? So when I talk about kind of having conversations with judges, I just mean in public through writing through. Yeah, I don't know.

I didn't mean to say, yes, you're on the phone telling them how to decide cases.

But you, but you are, you do seem, I mean, they cite your scholarship.

They argue with it. You're dealing with with doctrine, I think more than the average law professor. So what is that about? So this is an area of law that judges really care about. And they come to it without an obvious set of assumptions about what the answer should

be, way more often than in other areas. So you know, a lot of law professors, I think, don't engage with judges out of a sense that sort of the judges won't listen. The judges aren't interested. They've come up with their view of what the answer should be.

And a lot of it is, I think, a lot of law professors want to write in areas where judges already have pretty strongly held views.

“And so try to persuade someone like, you know, you should be in favor of Roe v. Wade or”

something like that. Like, guess what? They're going to have that conversation decades earlier and they're not going to change their mind because you cited some neat philosopher. That's just not how people think through hard legal issues.

But when it comes to this, it turns out, and I just, I didn't, I wasn't really expecting this when I started writing in this area. But I was just delighted that it turns out a lot of judges say, well, this seems important. Like, I might decide a lot of cases and the one about new technology is going to set a precedent.

It's going to matter. And I want to get it right. It's just not obvious what the answers are. You could be a conservative originalist and you could be, you know, left of center or living constitutionalists, whatever your views are.

They're actually all kind of coming to these issues with that same sense of like kind of history is is looking at them. This is going to be one of their important opinions they want to get it right. And so they engage with scholarship a lot more than they would in other areas.

“I guess I think if it's, it's like an amazing area of law and that judges are, they're”

acting in good faith really trying to figure out what the answer should be way more than law professors usually give judges credit for, you know, we're pretty, pretty cynical group among law professors. So, so in a lot of ways, my scholarship is directed to them to that audience of the folks actually making the decisions assuming they are actually thinking through it in in good

faith which they really are and that just just like, okay, where's this going to land? And let's think through this. And you know, sometimes judges are not happy when you criticize something that they do. But, you know, by and large, it's, in a lot of ways, I think of it as this is a throwback to the 1950s, 1960s notion of, you know, academics following the courts, courts following,

you know, that conversation happening, we've kind of left that model behind and I just think it's, there's a lot more to it that, that I think a lot of law professors could benefit from trying out. You've written a lot of scholarship on these topics and law re-articles and blog posts and things like that over the last quarter century and now you've written a book.

You've written a book that's kind of technology dependent, I mean, a lot of the arguments in the book are the state of technology circa early 2025. So I guess I'm wondering and the books also it seems to me written for a little bit more general audience than your law re-articles. So I guess the question is, why write a book now and how do you think about the problem

I mean, you're going to have second and third editions every seven or eight years.

“So I wrote the book because I had written a lot of individual articles over time, which”

were quite narrow. What I like to do in writing a law re-article is write it on a discrete doctrinal issue, kind of have it be instead of it being a lot of law professors write these grand theory articles and like everyone should rethink the way they think about law in 50 pages or something like that.

And what I like to do is have like a really narrow, like here's an issue that's come up, you know, the scope of computer warrants or should you try to regulate how a search is executed in the warrant itself. Something like that really discreet little issues. And I do that in part because, you know, I assume that judges, law clerks, litigants, like

they have a legal issue and they can see that article and say, aha, that's actually really helpful for me. And I can give my normative take in that, but that's, it's designed to be kind of helpful to that audience. And I thought, well, there's benefit to taking, instead of writing on all these little

narrow issues and using the method in these narrow issues of writing a one big picture book that says, well, here's the, here's the overall kind of big picture of what's going on. And we're going to play that out. So the first third of the book is like, here's the method.

And then the second middle part of the book is about, here's what searches and seizures

are in the standalone environment. Here's what a search is or here's what, here's how the border search exception might apply for example, to digital devices, which I argue it should not apply to digital devices. And then the last third is the network problems of hand. And so the thought is, if you have just a one book that sort of gives the whole big picture,

that really you can give people an idea of the big direction, the big shift that's occurring in a way that you're not going to get from just these individual discrete articles.

“I mean, in terms of whether it's going to be outdated, you know, I think a lot of these”

issues have been around for a long time, surprisingly, that we, we talk about technology changing really rapidly. And a lot of ways, new issues come up, but the old issues don't go away in a way that we might expect. So, you know, the Supreme Court's never decided to case on Fourth Amendment rights in email, email has been around for a really, really long time.

And so the technology is, is evolving, but a lot of the big questions are around. And they're going to stay around for, I think, decades to come. Sure, they will. The last question is, so I thought you were very successful in going up a few thousand feet in this book, compared to your articles.

And in kind of laying out in one place, what the Fourth Amendment is, how it normally works, here's the basic doctrine, here's the equilibrium adjustment theory, and here are a whole bunch of applications in the digital realm. I find that when I have written books that do something like that, that try to take other things I've written and kind of stitch them together, and some sense add some parts.

And we've it all together, I find that I had to rethink things sometimes, or I learned something new. And you also dealt with some new issues in this book. I'm wondering if there was anything in the process that sticks out, that you realized that you didn't realize before, or that you had some insight in the course of putting this

together, or some adjustment to your way of thinking about things. So in writing the book, I made a point of not going back and rereading the articles. So I wanted it to all fit together of my kind of current thinking rather than, here's

what I said in 2005, and here's what I said in 2010.

And so there are ways in which the arguments end up coming out a little bit differently, absolutely. So I have a chapter on the rules for search warrants, and digital warrants, and how to limit the scope of a digital warrant. And I end up in the same basic place of this, you know, I wrote an article on this in 2005,

“in another 2015, but the argument I think now is a lot tighter and fits together with other”

arguments a lot better than it was in those earlier efforts. So I think I have a line in there to the effect of like, hopefully these are improvements on the prior views, but yeah, I made a point of not going back and just trying to give the whole picture today without reference to all those old articles. Well, it's very successful.

Congratulations, Warren. Thanks so much, Jack. The Law Fair podcast is produced in cooperation with the Brookings Institution. You can get ad free versions of this, another law fair podcast by becoming a law fair material supporter through our website, law fairmedia.org/support.

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“A theme song is from Haliby Music, as always, thank you for listening.”

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