Jacob Sullum on Warrantless Cellphone Tracking

In January the Supreme Court unanimously ruled that tracking a suspect's movements by attaching a GPS transmitter to his car counts as a "search" under the Fourth Amendment. But because the majority opinion emphasized the physical intrusion needed to surreptitiously install the transmitter, it did not resolve the constitutional implications of surveillance using cellphones, the tracking devices that Americans voluntarily carry in their pockets and purses. In the absence of clear guidance, says Senior Editor Jacob Sullum, law enforcement agencies are making up the rules as they go along, often obtaining location data from cellphone carriers without a warrant even for routine investigations. Last week a House subcommittee considered a bill that would address this threat to privacy by requiring a warrant for geolocational surveillance, regardless of the method used.