(FOX NEWS) - An electronic device that tricks cellphones into revealing a user's location is becoming a key weapon for law enforcement in its battle against drug traffickers, terror suspects and other dangerous criminals -- but its potential misuse against innocent Americans and the secrecy surrounding which agencies have the devices is of growing concern by civil liberties watchdogs and lawmakers.
Cellular site simulators -- known as "StingRay tracking" -- basically are fake cell towers that use digital signals to trick a cellphone into revealing its location and other information. Law enforcement typically places the device near the location of a known suspect -- but they also have been used at large gatherings such as rallies, where the digital information of hundreds, even thousands, is scooped up.
And while law enforcement agencies turn to the courts for permission to deploy the devices, the requests typically are generic applications called "pen register applications," which only require the agency to affirm that the device will be used in a criminal investigation, without having to name a specific individual. That legal vagueness is what concerns lawmakers.
"If you can track somebody's location 24/7, you know the content of their life," said Rep. Jason Chaffetz, R-Utah. "I think innocent Americans have a reasonable expectation of privacy."