Triggerfish, also known as cell-site simulators or digital analyzers, are nothing new: the technology was used in the 1990s to hunt down renowned hacker Kevin Mitnick. By posing as a cell tower, triggerfish trick nearby cell phones into transmitting their serial numbers, phone numbers, and other data to law enforcement. Most previous descriptions of the technology, however, suggested that because of range limitations, triggerfish were only useful for zeroing in on a phone’s precise location once cooperative cell providers had given a general location.

This summer, however, the American Civil Liberties Union and Electronic Frontier Foundation sued the Justice Department, seeking documents related to the FBI’s cell-phone tracking practices. Since August, they’ve received a stream of documents—the most recent batch on November 6—that were posted on the Internet last week. In a post on the progressive blog Daily Kos, ACLU spokesperson Rachel Myers drew attention to language in several of those documents implying that triggerfish have broader application than previously believed.

More details on Ars Technica