Let’s Be Reasonable About Geofence Warrants

For years, I wrote a lot about the Fourth Amendment and new technologies (see summary in this note 6), so I was very pleased with the inflection point Carpenter v. United States, 585 U.S. 296 (2018), and I am naturally chuffed when the courts grapple with my work.  So, I certainly appreciate the Fifth Circuit using a bit of that work in United States v. Smith, 110 F.4th 817 (5th Cir. 2025), most recently repeated in In re Four Applications for Search Warrants, No. 3:25-CR-38-CWR-ASH (S.D. Miss. Feb. 21, 2025).  However, to the extent those courts categorically prohibit cell tower dumps (or “extractions”) and similar geofence requests as per se unreasonable general warrants, that is a step too far.

As I have developed elsewhere (Part II here and summarized in this recent keynote), the Founding dislike of general warrants was rather astoundingly personal, and not all that impressive—I mean, when you are smuggler, you don’t like the laws that catch you, right?  And so it was that what was routine in England became despised in America.  But it’s 2025 now, and we don’t have a crown across the sea bothering us about repayments that we normatively owe but don’t want to pay.  (See OverSimplified’s wonderful video, beginning around the 2:30 mark.)  And we have police… lots and lots of them.  And we have criminals… surely too many of them.  And some are dangerous.

So, at least for that dangerous subset, let’s not be James Otis hotheads and John Adams egotists.  Let’s be reasonable, which is not only the Fourth Amendment textual command, but in this context is actually rather straightforward.  Yes, warrant applications for cell tower dumps can satisfy probable cause and particularity if their protocols adequately leverage selective revelation to ensure that solely records for which we algorithmically have fair probability of criminality make their way to police.  The warrant applications in In re Four Applications didn’t do that.  But when warrant applications do, they ought to be approved, as I explain here.

The Fourth Amendment’s designedly ambiguous command has seen us through hundreds of years of remarkable social and technological change.  The third-party doctrine was a far-too-long-monolithic speedbump in that road, but the solution is not equally monolithic unreasonableness on the ‘other side.’