Lawfare: Do Geofence Warrants Violate the Fourth Amendment? by Nathaniel Sobel:
Last year, a New York Times feature detailed law enforcement’s use of a new investigative technique called a geofence warrant. Unlike traditional warrants that identify a particular suspect in advance of a search, geofence warrants essentially allow the government to work backward. These warrants compel a technology company (so far, only Google) to disclose anonymized location records for any devices in a certain area during a specified time period. After that, for certain accounts, the government may obtain additional location data and subscriber information. Particularly in light of the Supreme Court’s watershed decision in Carpenter, geofence warrants present a host of novel Fourth Amendment issues.