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.

Pen register devices only need court orders for use, meaning that government agents are required to meet a lesser standard than when applying for a full search warrant. However, the Stingray may not fit the definition of a pen register because it collects location data; and the appropriate requirements for using one have been determined on a case-to-case basis. Though the newly revealed documents make it clear that judges are now more aware of the device's use, it's unclear if federal agents' failure to properly detail their use of the device has been resolved.

What other information the Stingray sweeps up while waiting for the target phone is also in question. The Electronic Frontier Foundation notes that the data of thousands of people may be collected by the Stingray, but because the agents who use the device have revealed little about how it works, it's not known what extraneous information is collected. However, federal agents have claimed that they delete any information retrieved that doesn't relate to their target. It may be a while before we learn how the devices truly operate, but the requirements for their use could be ruled on soon: the ACLU and EFF have filed amicus briefs for Thursday's case, and alongside other civil liberties organizations, are certainly interested in seeing the first hard ruling on the requirements for a Stingray's use.