A geofence warrant inverts the traditional warrant process. Instead of naming a suspect and then seeking their records, police define a geographic perimeter and time window around a crime scene, then compel companies like Google to produce location data for every device in the area. Officers review the anonymized results, narrow the pool, and attempt to identify suspects. The technique grew rapidly since 2017. It raises Fourth Amendment questions because it captures data from innocent bystanders who happened to be nearby.