What just happened? A recent Supreme Court decision puts new limits on how police can use smartphone location data, a tool that has become increasingly common as digital tracking grows more precise. In Chatrie v. United States, the Court ruled 6-3 that using a geofence warrant qualifies as a search under the Fourth Amendment. As a result, police use of these warrants is now subject to constitutional limits and judicial oversight.
Geofence warrants work differently from traditional investigations. Instead of starting with a suspect, police define a specific place and time, then ask a company to provide data on all devices in that area. From there, investigators narrow the list and may request identifying details for certain users.
The case centers on a 2019 robbery at a credit union in Virginia. Police asked Google for data on devices within a roughly 500-foot radius of the building during a one-hour window. Google initially provided anonymized data for 19 users. Investigators later asked for more details, and the company identified three people, including Okello Chatrie. His location history became part of the case against him.
The decision draws on the Court's 2018 Carpenter v. United States case, which found that people retain a privacy interest in cellphone location records even when a company stores them. This latest ruling extends that idea to geofence warrants, recognizing how much can be learned from tracking where a device has been.
Today's phones combine GPS, Wi-Fi, Bluetooth, and cellular signals to generate detailed location data. That data can sometimes locate a device within meters and can be collected continuously and stored for long periods.
"It's not just collecting location when you're trying to call an Uber," Serge Egelman, a privacy researcher at the University of California, Berkeley, told Scientific American. "It's sharing location data throughout the day, whether you intend to or not."
Use of geofence warrants has expanded quickly. Google reported receiving its first such request in 2016. By 2020, that number had grown to more than 11,000. And Google is only one source. Many apps, including social media and mobile games, collect location data that can be shared with third parties or accessed by law enforcement.
What has changed is not just the amount of data, but how easily it can be used. Instead of following a suspect in real time, investigators can now look back and reconstruct movements after the fact. They can identify which devices were near a location, then trace where those devices went before and after.
"When the costs dramatically drop by orders of magnitude, law enforcement might be more prone to use it all the time," says Jason Hong, a computer scientist at Carnegie Mellon University.
The Court's ruling does not ban geofence warrants. Police can still use them if they obtain a warrant supported by probable cause. The justices also did not decide whether the warrant in this specific case was valid, leaving that question to a lower court.
The decision could have broader implications. Other surveillance systems, such as networks of cameras that monitor public spaces, raise similar concerns about how much information can be gathered and analyzed at scale.
"Systems of mass surveillance, like real-time crime centers that have cameras on every street corner, create the exact same problem," says Andrew Guthrie Ferguson, a law professor at George Washington University. He added that "Chatrie plants the seeds for arguments that other forms of mass surveillance might also require a warrant."
At the same time, the technology behind location tracking is shifting. Google has started storing more location data directly on users' devices rather than on centralized servers, which could make broad data requests harder to fulfill. But the wider ecosystem remains complex, with many companies still collecting and sharing location information.
The ruling sets a constitutional checkpoint, but it does not ban the technology or clearly slow its use. Judges approve most warrant requests, which raises questions about how much practical change this decision will bring. As Ferguson puts it, warrants can act "less as a shield than a key."
The Supreme Court just ruled that police need a warrant to use phone location data
