The Supreme Court has now heard arguments in Chatrie v. United States. So, we’ll soon learn more about the Fourth Amendment restrictions on geofence warrants. And, as teachers, we’ll debate how to pronounce ‘Chatrie.’
And let me not bury the lede—Chatrie ought to hold that reverse warrants such as this are not per se unconstitutional general warrants, but that their selective revelation process used to satisfy Fourth Amendment reasonableness must be regulated by the magistrate, not by a private party and not by police. Basically, the search warrant process in this case was controlled by Google, when the Constitution of course requires it be controlled by a court.
Okay… we need to make it there. So, returning to our story… the pronunciation of ‘Chatrie.’ Now, that’s not terribly important. But there’s actually quite a lot about Chatrie that isn’t terribly important. First, everyone seems to believe the defendant is going to lose in the sense that no suppression is going to happen. These officers reasonably relied upon a warrant issue by a neutral and detached magistrate, and that means no suppression under the horribly mistitled ‘good faith’ exception to the exclusionary rule. (I’ll always remember a co-defendant in Carpenter reaching out to me after that decision, upset that he was the ‘left behind.’ But no… Timothy Carpenter didn’t win what that gentleman understandably thought Timothy had won.)
Second in what ‘doesn’t matter’: Google has shut down its inane Sensorvault, the database at issue in Chatrie. That Chatrie is a Sensorvault case, as opposed to a more typical geofencing or other ‘reverse warrant’ case, leads to potential conclusions that typically wouldn’t make good sense, such as Justice Roberts wondering why this isn’t simply a case of the defendant not “clos[ing] [his] window or the shades,” and Justice Alito wondering why it’s a constitutional issue when the defendant “had to go through multiple steps in order to turn [this data storage] on.”
Thus, Alito wasted little time asking Adam Unikowsky—counsel for Chatrie and one of the most thoughtful Supreme Court advocates of our day—whether this mess was even worth the candle.
Alito: Mr. Unikowsky, I’m struggling to understand why we are hearing this case other than the fact that at least four of us voted to take it. (Laughter.)
That’s a pretty good line. But no, Justice Alito, a defense win would not be “an advisory opinion,” as the Justice then asserted, lest our Fourth Amendment rights ossify in a blinding mess of reasonable reliance decisions that never decide any of the things most important. We’ve been down this road before… looking at you, Davis v. United States, 564 U.S. 229 (2011), carving an exception to the Court’s exception to the Court’s exclusionary rule, permitting a winning defendant who first changes a rule to potentially get suppression. The better analysis realizes the merits case and controversy—indeed, it rarely gets more important than establishing the parameters of the people’s Fourth Amendment rights—even if this particular defendant’s remedy then remains to be determined.
So, please don’t toss the baby with the bathwater and dismiss certiorari in Chatrie as improvidently granted. We need to hear from you, Supreme Court, on the geofencing issue. I first wrote about cell tower dumps in 2013, and, in a sense, the OG Christopher Slobogin has been writing about the underlying principles since the 1990s. So, no DIG!
Still… please also don’t “embarrass the future.” When you get something constitutionally wrong, Supremes, it sticks with us for a long, long time. You did it in Miller and Smith in this Fourth Amendment context, and it took until Carpenter to begin remediation. (I develop that point here.) So, moderation is wise. Here’s Justice Frankfurter giving us the “embarrass the future” line:
To what extent [a tax apportionment rule] should be carried over to the totally new problems presented by the very different modes of transportation and communication that the airplane and the radio have already introduced, let alone the still more subtle and complicated technological facilities that are on the horizon, raises questions that we ought not to anticipate; certainly we ought not to embarrass the future by judicial answers which at best can deal only in a truncated way with problems sufficiently difficult even for legislative statesmanship.
That wisdom certainly applies to the geofence. We need—but still lack—legislative statesmanship. (Is that even a thing anymore?!)
So, how to hit the Chatrie sweet spot? Fix what was definitely wrong and that otherwise will be repeated. Fortunately, a number of Justices hit upon just such a middle path in the Chatrie arguments.
First, the Court should reject the extreme, unhelpful view that all geofence warrants are per se unconstitutional general warrants. Yes, Fourth Amendment particularity was designed to prohibit the Founding-era general warrant, and yes that has very important implications still today. (I review that history and some of its implications here, and dang if it isn’t a fantastically human story.) But restricted, automated review of digital databanks in 2026 is not the same as authorizing a constable to look wherever she wishes for lost sheep or uncustomed goods in 1791. It ought to be enough to state the matter. There is no meaningful Founding equivalent to a binary search of a database that returns solely a ‘yes’ or ‘no,’ and doesn’t require a human privacy-invasive combing through. Originalism—asking, say, how would a learned reader understand a provision when drafted—can be very useful. But it can also teach next to nothing when after-arising technologies and social norms have changed nearly every relevant criterion, such that at best we can hope to translate that earlier intention to our very different day. Fortunately, reading the tea leaves of oral argument, I don’t see a Chatrie Court willing to reject all geofence and similar ‘reverse searches.’ In the words of Justice Sotomayor, a Court ‘liberal’:
That’s not what this does. This identifies a place, a crime, a limited time frame but a time frame, so it’s not a general warrant in a historical sense.
Indeed, I’d say Unikowsky conceded as much when he accepted geofence searches in the emergency case: an emergency lessens the justification necessary for a search, sure (e.g., lessening probable cause not merely to reasonable suspicion but even further to ‘reason to believe’), but there is no reason to think emergency would permit per se unconstitutional general searches.
So, so far so good. The Chatrie Court should reject a per se ban on ‘reverse warrants,’ and I think it will.
Second, the Court should reaffirm our constitutional design, which is that a magistrate—not a private party being searched, and certainly not the police searching—must specify the grounds under which a desired police search is reasonable. I’ve posted previously on how I’d approach the geofence question (one, two, three, four, and five). But not all that can be helpfully resolved in Chatrie, including because it will be too hard to ‘count to five.’ Instead, it would be wonderful to see a unanimous Court strike down this warrant because its ‘Steps 2 and 3’ unconstitutionally delegated the magistrate’s task to the very police searching and the very party being searched.
Unikowsky nicely established just this framing in the introduction to his argument. After quickly urging that this was a general warrant (it’s meaningfully not) and that there was not probable cause (it’s debatable as there was minimization but perhaps not enough), Unikowsky urged this:
Finally, at step 2 and step 3, the search violated the Fourth Amendment because the warrant gave the police unlimited discretion to decide who to search while casting Google into the role of magistrate.
I welcome the Court’s questions.
Amen on the substantive point. Amen on the artful phrasing: casting Google into the role of magistrate. And amen on the skilled oral advocacy of quickly getting out one’s argument and then letting the Justices get to work. As I said, Unikowsky is one of the best.
Unikowsky later followed with this:
I don’t think there’s particularization here when the warrant just said, whatever unspecified number of people are in the proximity of the crime, those are the people to be searched.
…
All [the warrant] said was the police are going to figure out the really suspicious people and they’re going to do those extra searches.
…
All [the warrant] says is that once the police winnows down the 19 or however many there are to some smaller number, then it can collect additional data. But that’s not particularized because it doesn’t say how to identify those people.
Quite right. Instead, the number of ‘hits’—if not preset by the judge—must return to the judge, who can then decide whether it is sufficiently few to meet the necessary justification threshold to satisfy Fourth Amendment reasonableness under the circumstances.
To use another Unikowsky example,
[S]uppose there is a murder in the woods and it’s 3 a.m. and there’s, you know, one criminal and one victim and you draw a circle around that and there really is probable cause to think that every single person in that circle is either the murderer or the victim, then maybe the government can say there’s probable cause that every person whose data is exposed to the government in that case will have relevant evidence.
That’s what a process of selective revelation can effectively achieve when it’s not a murder in the secluded woods at 3 a.m. (because, you know, not all murderers are quite so kind to criminal investigation): selective revelation permits the private party computers to work the data without exposing anything to the State until the hit numbers satisfy the justification standard.
Thus, Justice Gorsuch’s slightly ‘softer’ example to which Unikowsky agreed:
Gorsuch: There might be probable cause to — to think that everybody in the bank [during a robbery] might have some information?
Unikowsky: Right. That’s right. If you can draw a small enough geofence at a small enough time interval that everyone there either committed the robbery or witnessed it, then you might say there’s probable cause that everyone has relevant information.
Again that seems right, and later Justice Kavanaugh would return Unikowsky to the same theme. Of course, police could not seize every bystander to a crime, at least in the ex post investigatory sense. But surely they can knock on every door or ping every phone-directory phone—that’s a reasonable cost of living in a relatively safe society.
So, we want meaningful magistrate control over the warranted-search process, and, fortunately, a number of Justices expressed something like a ‘reaffirm the magistrate’s role’ view. Motivating Unikowsky’s failure-of-particularity arguments quoted above, Gorsuch directly asked, “Would that be a narrow basis on which to resolve this case?” And Justice Jackson later echoed the theme, looking for trial court direction regulating “Google’s iterative process for giving the officer this information.” During the State’s argument—after Justices peppered away at hopeless brick-and-mortar analogies—Jackson returned to this: while the police in this case didn’t explain to the magistrate why it was reasonable to draw the geofence circle at this size and for this time, they could have done and should have done. That’s how the magistrate decides whether the requested search is constitutionally reasonable. Justice Sotomayor later picked up on the same, noting that in many jurisdiction police are going back to the court during the selective revelation process. Not only did the State not think such a move unduly burdensome, “with more recent warrants, the government has done that.” Bingo.
Which led Sotomayor to lay it out like this:
And wouldn’t that have value for the dispute that’s going on around the country and between and among judges even on this Court? Some said there was — some took your position that there’s no right of privacy whatsoever and you don’t need a warrant. Others have taken the position that you need a warrant, but you don’t need much supervision from the magistrate judge. There is value in our setting the parameters of this process, isn’t there?
Again, the respondent not only didn’t disagree, he conceded that, “We’ve actually done that in more modern times.” Excellent.
Later, Justice Kavanaugh urged much the same, while also urging that just as reviewing courts defer to a magistrate’s determination of probable cause (Illinois v. Gates’ “substantial basis” review), reviewing courts ought to defer to the magistrate in the particulars of the selective revelation process. So long as the magistrate—and not the police and not the private party—is reasonably running the show, I agree.
With this, Chatrie can be a significant Fourth Amendment win that will not embarrass the future. Litigation will continue, yes, and I have previously expressed my views on how selective revelation can do the necessary work, as have others (including forthcoming work by Jordan Wallace-Wolf that I would recommend). But with this hoped-for Chatrie guidance, it will be better policing—and better litigation—than before. And when the issue next reaches the Supremes (and it will), everyone will be ready to take the next constitutional step.
In short, a magistrate needs to oversee the warrant selective revelation process, not merely outsource its substantive decisions to a private party. So, this warrant was bad—albeit reasonable reliance makes for no suppression—and our Fourth Amendment world takes one step forward.
(Given my post’s focus, I’ll not belabor why I think other Chatrie resolutions could do great harm. But, for example, while Unikowsky understandably argues ‘anonymization is meaningless’—understandably because here the argument helps his client—any argument that removes smart magistrate-driven selective revelation from these investigatory contexts would be a massive loss. And Justice Kavanaugh thinking that Zurcher permits search of any size database so long as there is probable cause to believe evidence of a crime somewhere therein? That runs up against my argument, picked up by the Fifth Circuit, that then any sufficiently large database could always be searched! By contrast, Unikowsky plugging (not saying ‘with attribution’ 🙂 ) my longstanding notion of a “limited third party doctrine” that constitutionally applies only to information provided for third party use would be a nice move in the right case. And there is a wonderful exchange between he and Justice Alito regarding grand jury subpoenas routinely searching through reams of different person information, to which Unikowsky could only “go back to the test in Carpenter,” because… nobody can do better given our lack of any actual rule! All of which is merely to say that much more can be said. But I’m hopeful Chatrie will say only a couple of things, and say them well.)
ADDENDUM 05.14.26
I ought to have mentioned that the Supreme Court of Minnesota held much as I am advocating, in an opinion interpreting the state’s Fourth Amendment analog. See United States v. Contreras-Sanchez, No. A22-1579 (Minn. 4/15/26).
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