The US Supreme Court ruled Monday that law enforcement agencies must obtain a warrant before searching a geofence, reaffirming that probable cause is necessary to subpoena cellphone location data.
Decision on Chatrie v. United States has held that users’ digital, device-based data is private and that the Constitution limits the government’s ability to access tracking data from technology companies. In a 6-3 decision (PDF) written by Justice Elena Kagan, the Supreme Court found that “a person has a reasonable expectation of privacy in records about his cell phone’s location” and that geofencing mandates “infringe on that constitutionally protected interest.”
Privacy experts welcomed the decision. Alan Butler, executive director of the Electronic Privacy Information Center, said in a statement after the decision: “EPIC applauds the Supreme Court’s recognition that warrantless geofence searches are fundamentally inconsistent with the Fourth Amendment’s protection against unreasonable searches and seizures.”
Geofence and Constitutional Warranties
Geofencing is usually done by law enforcement officials when a case has no clear suspects. The police will draw a shape on a map at the scene of the crime, specify a window of time for questioning and issue a geofencing warrant to the tech giant asking for information about any connected devices present between those elements during that time.
After checking this information with any suspects or suspicious persons, the police can subpoena additional account information (email addresses, phone numbers, usernames and more) related to devices within the geofence.
The Court’s ruling found that users don’t voluntarily share their private information with a company like Google, meaning that the third-party doctrine (PDF) — the legal principle that says people have no expectation of privacy when it comes to voluntary sharing — doesn’t apply.
As a result, the Fourth Amendment, which prohibits unreasonable searches and seizures, protects against the current iteration of geofencing warrants. Those warrants are less strict and have fewer legal guidelines than regular search warrants.
Sadly, the Supreme Court did not outright block the enforcement of geofencing; rather, police must have probable cause regarding a suspect and obtain a search warrant to use geofencing data sparingly.
Critics point out that geofencing not only traps potential suspects but harvests the location data of everyone in the area. In cases where law enforcement draws a border around a large area of the map, the agency may request information about millions of people at a time.
Geofencing has been referred to as a form of reverse search, as authorities use location data to pinpoint a crime to a suspect, rather than naturally finding evidence that would suggest the suspect was in the area when the crime was committed.
Google, one of the most popular technology companies, has taken its own measures to protect itself against geofencing warrants in recent years, removing users’ location data from Sensorvault servers and moving it to users’ devices. However, police can still issue warrants to private individuals to call up location information from their phones.
If this doesn’t sound like a familiar type of geofencing, that’s because the term is used to describe several use cases for location-based technology. It can also refer to the technology behind smart home controls or the advertising practices of Big Tech. The Supreme Court decision applies only to mandates.
How did this case come about?
The case that went up to the Supreme Court was based on the case of Chatrie v. United States (PDF). The plaintiff in the case, Okello T. Chatrie, was arrested in 2019 after police linked him to a $195,000 bank robbery. Law enforcement requested data from Google, finding bank devices during the heist. The list of good suspects was reduced from 19 people to three, eventually leading to Chatrie’s arrest.
Chatrie’s attorney, Adam Unikowsky, said (PDF) police had no reason to gather his client’s information, instead turning to “tools that allow the government to search first and reveal allegations later.”
Even if the data were obtained without a geofencing search, Unikowsky argued (PDF), a search warrant would be unconstitutional because probable cause would not exist to “search the private physical documents of every single person within the geofence simply because of proximity to the crime.”
It’s unclear how the new precedent could affect the outcome of previous cases, including Chatrie’s. Previous courts ruled that Chatrie’s sentence would not change because the geofencing evidence was obtained in good faith, but the Supreme Court’s decision leaves the validity of the warrant in question.
Chatrie’s case returns to a lower appeals court, which will decide whether there was probable cause for the geofencing warrant. A representative for Chatrie’s legal team did not immediately respond to a request for comment.
