404 Media has obtained material that explains how Tangles and Webloc, two surveillance systems ICE recently purchased, work. Webloc can track phones without a warrant and follow their owners home or to their employer.

A social media and phone surveillance system ICE bought access to is designed to monitor a city neighborhood or block for mobile phones, track the movements of those devices and their owners over time, and follow them from their places of work to home or other locations, according to material that describes how the system works obtained by 404 Media.

Commercial location data, in this case acquired from hundreds of millions of phones via a company called Penlink, can be queried without a warrant, according to an internal ICE legal analysis shared with 404 Media. The purchase comes squarely during ICE’s mass deportation effort and continued crackdown on protected speech, alarming civil liberties experts and raising questions on what exactly ICE will use the surveillance system for.

“This is a very dangerous tool in the hands of an out-of-control agency. This granular location information paints a detailed picture of who we are, where we go, and who we spend time with,” Nathan Freed Wessler, deputy project director of the American Civil Liberties Union’s (ACLU) Speech, Privacy, and Technology Project, told 404 Media.