Federal agents regularly used a cellphone location tracking device known as a Stingray without informing judges of their intent to do so, the American Civil Liberties Union revealed in a newly obtained document. The practice of using the device without a search warrant may be ruled on in a case that's set to go on trial in federal court this Thursday. The newly uncovered documents reveal that this undocumented use occurred until at least 2011, when emails from the US Attorney's Office were sent out expressing the "collective concerns" of magistrate judges upon discovering the practice. CNET reports that the devices were in use as early as 2008 in Arizona and Wisconsin, but that the technology goes back to the mid-1990s. Judges are questioning if the Stingray's location tracking abilities mean that the device violates Fourth Amendment rights when used without a search warrant.

The legal requirement for using a Stingray is still uncertain

According to The Wall Street Journal, the Stingray operates by simulating a cellphone tower: when a target's phone connects to it, it then waits for additional signals, and eventually uses triangulation to determine the phone's location. From that point forward, the Stingray's operator can find the phone's location as long as it remains powered on. Agents looking to use the tool have reportedly only requested a judge's permission to use a "pen register," a type of device that can detect phone numbers that have been dialed, but not location.