On 22 June 2018, the United States Supreme Court issued their ruling in the Carpenter case.
The case could have some application for military practitioners. The use of digital forensic evidence is becoming increasingly common. Law enforcement often seeks to examine cell phone data, computer hard drives, phone company records, and now GPS data. We've certainly seen military cases in the past where the Army sought to obtain geolocation data from a phone company.
Carpenter asked the question whether the Government conducts a search under the Fourth Amendment when it accesses historical cell phone records that provide a comprehensive chronicle of the user's past movements.
Spoiler alert. The short answer for the Supreme Court was yes. There is a reasonable expectation of privacy in your location information. In Carpenter, ironically, the defendant and his accomplices robbed some Radio Shack stores and T-Mobile stores in Detroit. A magistrate ordered Sprint to provide Cell-Site Location Information (CSLI). Long story short, Carpenter's buddies all rolled on him and claimed he was the ring-leader. The Government obtained the CSLI without a warrant.
Under this ruling, the government must obtain a warrant before obtaining Cell-Site Location Information.