Recent reports about the Secret Service and Immigration and Customs Enforcement playing fast and loose with rules regarding cellphone tracking and the FBI purchasing phone location data from commercial sources constitute an important wake-up call. They remind us that those handy mobile devices many people tote around are the most cost-effective surveillance system ever invented. The United States Secret Service and U.S. Immigration and Customs Enforcement, Homeland Security Investigations (ICE HSI) did not always adhere to Federal statute and cellsite simulator (CSS) policies when using CSS during criminal investigations," the Department of Homeland Security's Office of the Inspector General reported last month. "Separately, ICE HSI did not adhere to Department privacy policies and the applicable Federal privacy statute when using CSS." The OIG report referred to the use of what is commonly called "stingray" technology"devices that simulate cellphone towers and trick phones within range into connecting and revealing their location. "They also gather information about the phones of countless bystanders who happen to be nearby," the ACLU warns. Even the most precise phone company location data remains available with court approval. The courts are currently mulling multiple cases involving "geofence warrants" whereby law enforcement seeks data not on individuals, but on whoever was carrying a device in a designated area at a specified time.