 Initially, the use of Stingray phone trackers was a secret, due to a number of non-disclosure agreements between individual police departments and the Federal Bureau of Investigation.According to the American Civil Liberties Union, the FBI entered into agreements with at least 48 police departments in the United States.In these agreements, the FBI allowed police departments to use the stingrays, while requiring police departments provide no information to either the public or the courts regarding the devices' operation or existence.