The U.S. Supreme Court has delivered a significant blow to law enforcement's use of geofence warrants, ruling that they require search warrants when seeking location data from tech companies like Google.

In a 6-3 decision, the court ruled that individuals have a reasonable expectation of privacy in their cell-phone location information, meaning authorities need a warrant to access this data. This applies even for historical geofence data requests, where law enforcement asks tech companies to search through vast amounts of user location data.

Chief Justice John Roberts argued that because users do not willingly share their location with Google simply by using its services, the third party doctrine does not apply here. Critics have long argued that these warrants are unconstitutional due to their overbreadth and potential inclusion of innocent people's data.

The court allowed police to narrow their requests when seeking a warrant but did not outright ban geofence warrants, setting the stage for future legal battles in appeals courts. The decision comes at a time when tech companies like Google are already storing location data locally on devices rather than servers, cutting off one avenue of law enforcement's data requests.