Senator Edward J. Markey (D-MA) has sent detailed questions to Attorney General Holder about recent reports that law enforcement agencies have deployed aircraft equipped with cell tower simulators to capture mobile phone communication. The devices, known as "IMSI catchers" or "Stingray," identify and track cell phone users. Senator Markey wrote "the sweeping nature of this program and likely collection of sensitive records...raise important questions about how the Department protects the privacy of Americans" with no connection to unlawful activities. EPIC successfully sued the FBI to obtain documents about the agency's use of Stingray devices. EPIC has also filed amicus curiae briefs in the U.S. Supreme Court and the Supreme Court of New Jersey arguing that location tracking is a search under the Fourth Amendment and should only be conducted with a judicial warrant. For more information, see EPIC: Locational Privacy and EPIC v. FBI (Stingray).