Supreme Court Rules Geofence Warrants Are Fourth Amendment Searches

Google received its first geofence warrant in 2016; by 2020 that number had passed 11,000, and the Supreme Court just drew a constitutional line around the practice—but not a ban.

6-3 Majority Extends Carpenter to Digital Dragnets

In Chatrie v. United States, the Court ruled 6-3 that a geofence warrant constitutes a Fourth Amendment search. Instead of starting with a suspect, these warrants let police draw a digital boundary around a time and place—say, a 150-meter radius around a credit union during a one-hour window—and demand location records from a company like Google. That 2019 Virginia robbery sweep returned data for 19 users; investigators narrowed it and arrested Okello Chatrie.

The ruling builds on Carpenter v. United States (2018), which held that people retain a privacy interest in their digital movement history even when stored by a third party. As Serge Egelman, a privacy researcher at UC Berkeley, puts it: phones aren't just sending location when you call an Uber—they're sharing it all day, whether you intend to or not.

The Numbers That Made the Ruling Necessary

More concretely, the volume has exploded. Google alone processes millions of location queries per year. The granularity comes from GPS, Wi-Fi, Bluetooth, and cellular signals fused to estimate position within meters. Apps like Instagram, Tinder, and even Candy Crush pull that data and can hand it over through legal demands or purchase—Google changed its Location History to store more data on-device, but it's only one collector.

The consequence: investigators can now rewind the movements of hundreds or thousands of devices days or weeks after an event, with minimal effort. Carnegie Mellon's Jason Hong notes that when costs drop by orders of magnitude, law enforcement uses the tool constantly.

Warrants as Keys, Not Shields

The Court stopped short of banning geofence searches. Police can still get location histories if they persuade a judge of probable cause. Andrew Guthrie Ferguson, a law professor at George Washington University, argues the decision plants seeds for challenging other mass surveillance systems, like real-time crime centers with cameras on every corner. But as Hong reminds us, judges approve the overwhelming majority of warrant applications—Ferguson calls warrants "less as a shield than a key."

Chatrie establishes a constitutional checkpoint, not a stopping point. The lower court still has to decide whether this particular warrant was valid. The real test will come when a judge considers a warrant for every device within a city block for a full day—and whether that scale still fits inside the Fourth Amendment.

Source: Supreme Court limits police searches of phone location data
Domain: scientificamerican.com