“Rayhunter works by intercepting, storing, and analyzing the control traffic (but not user traffic, such as web requests) between the mobile hotspot Rayhunter runs on and the cell tower to which it’s connected.”
EFF’s Rayhunter turns a $20 hotspot into a Stingray detector. Cell site simulators sweep every phone in range, not just the target’s. Police have hidden their use for years. Now anyone at a protest can check.