Modern cellphones are vulnerable to attacks by governments and hackers using rogue cellular transmitters called IMSI-catchers. These surveillance devices can precisely locate phones, and sometimes eavesdrop on communications, send spam, or inject malware into phones.

Recent leaks and public records requests have revealed that U.S. law enforcement in Baltimore, Milwaukee, New York, Tacoma, Anaheim, Tucson, and others have used IMSI-catchers extensively in vehicles or aircraft to identify and locate suspects.

These powerful surveillance devices have often been used with little to no judicial oversight. To provide transparency and accountability, we need independent information on who uses them, how often, and when.