GoKawiilThe US Supreme Court ruled on Monday that law enforcement agencies must obtain a valid warrant before conducting geofence searches, reaffirming that probable cause is required to subpoena cellphone location data.
The decision in Chatrie v. United States held that users' digital, on-device location data is private and that the Constitution places limits on the government's ability to access tracking data from tech companies. In the 6-3 ruling (PDF) written by Justice Elena Kagan, the Supreme Court found "an individual has a reasonable expectation of privacy in records about his cellphone's location" and that geofencing warrants "intrude on that constitutionally protected interest."
Privacy experts celebrated the decision. Alan Butler, executive director of the Electronic Privacy Information Center, said in a statement after the ruling: "EPIC applauds the Supreme Court's recognition that warrantless geofence searches are fundamentally incompatible with the Fourth Amendment's protections against unreasonable searches and seizures."
Geofence warrants and the Constitution
Geofencing is generally carried out by law enforcement officials when a case has no clear suspects. Police will draw a shape on a map around a crime scene, specify a time window to inquire about and serve a geofencing warrant to a tech giant requesting information about any connected devices present within those fences during that time.
After cross-referencing this information with any suspects or suspicious individuals, police can subpoena additional account details (email addresses, phone numbers, usernames and more) associated with devices within the geofence.
The Court ruling found that users are not necessarily voluntarily sharing their private information with a company like Google, meaning the third-party doctrine (PDF) -- a legal principle that states people have no expectation of privacy when it comes to data willingly shared with others -- does not apply.
As a result, the Fourth Amendment, which prohibits unreasonable searches and seizures, protects against the current iteration of geofencing warrants. Those warrants are far less stringent and have fewer legal guardrails than traditional search warrants.
Crucially, the Supreme Court did not outright ban law enforcement geofencing; rather, police must already have probable cause about a suspect and obtain a search warrant to use geofencing data more narrowly.
Critics point out that geofencing doesn't just ensnare potential suspects but harvests location data from everyone in the area. In cases where law enforcement draws a border around a large chunk of a map, an agency may be asking for information about millions of people at a time.
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