The U.S. Supreme Court ruled 6-3 (PDF) in Chatrie v United States (No. 25-112) that geofence warrants sweeping up smartphone location data constitute searches under the Fourth Amendment. The Court found that individuals have a "reasonable expectation of privacy" in such data, even when the tracking covers only a brief period or records movements in public. "An individual has a reasonable expectation of privacy in records about his cell phone's location, and police intrude on that constitutionally protected interest when they demand the information -- even though for only a limited time, and from a third-party tech company," wrote Justice Elena Kagan. Longtime Slashdot reader schwit1 submitted the story. The Guardian reports: The use of geofence warrants is widespread, and gives law enforcement agencies the power to compel tech companies to hand over sensitive cell phone data from people at or near crime scenes. The warrants allow police and the FBI to collect this information from individuals within the radius of a virtual "fence" during a particular timeframe. But they are not restricted to requesting data for precise targets.

The Chatrie case focuses on local police's pursuit of an armed bank robber in Richmond, Virginia. He fled with $195,000. Law enforcement tracked Okello Chatrie down through their use of geofence warrants. Chatrie had opted in to an optional Google "location history" feature that documented his location every few minutes. He was eventually sentenced to 12 years in prison, after pleading guilty. Chatrie's lawyers argued that this search was overly broad and violated his fourth amendment rights, which protects individuals from "unreasonable search and seizure." Lawyers said that police's use of geofence warrants amounted to an official "search" under the fourth amendment, and didn't meet the constitution's requirements for one.

The government had argued that accessing only a short amount of cellphone location information means this tactic does not count as a fourth amendment search and accordingly, should not be afforded the same privacy protections. But the judges in the majority disagreed. The judges in the majority opinion also wrote that the government's characterization of generating location history as a voluntary choice is "meritless." They suggested that people aren't choosing to share private information with third parties and the government "just by doing the ordinary thing cellphone users do." "The point of carrying smartphones is to use what is on them," including the apps and services they provide -- many of which use location data to customize a user's experience, they said.

[...] While the majority opinion noted that police conducted a fourth amendment search by accessing Chatrie's location history data, they noted that the court of appeals will weigh in on whether the "search was reasonable, meaning that each of its steps was properly described with particularity and found to be supported by probable cause." Law enforcement has said they need geofence warrants to find suspects and witnesses -- after reaching dead ends. The US government, for its part, has argued that people can't have a "reasonable expectation of privacy" when they are in public and have allowed a third party company, such as Google, to collect and analyze phone location data.