The equipment also sends intrusive electronic signals through the walls of private homes and offices, learning information about the locations and identities of phones inside. Initially the domain of the National Security Agency (NSA) and other intelligence agencies, the use of stingrays has trickled down to federal, state and local law enforcement. In one Florida case, a police officer explained in court that he „quite literally stood in front of every door and window“ with his stingray to track the phones inside a large apartment complex.