As reported on BuzzFeed, in our world of ever-increasing surveillance, you may have heard of devices known as “Stingrays,” or more properly IMSI (International Mobile Subscriber Identity) catchers. These devices act like a cell tower, and trick “unsuspecting” phones into connecting to them. They can then pass along where phones, and thus their users are, and in some instances even log communication.
It’s a scary thought, and according to the ACLU, 24 states are known to own IMSI catchers. Though they may visually blend into the urban environment, these devices do give off several tell-tale signs that they are operating in the area. Though still in a prototype form, engineer Ash Wilson has been experimenting with a device called SITCH (Situational Information from Telemetry and Correlated Heuristics) to identify when Stingrays are in operation.
The device uses a FONA SIM900 GSM modem, along with a Raspberry Pi and GPS receiver, to compare the unique identifier of each cell tower — or more properly, “base station” — in the area to those known to be in the area. If a new “tower” just happens to pop up one day, there is a good chance that it’s an IMSI catcher, though this could also indicate new construction. These devices also looks for unusually powerful “towers” in the area, meant to make cell phones in the area connect to it instead of legitimate base stations.
Though the system is far from bug-free, when it detects unusual signals, it triggers alarms via Slack. In theory, a network of these devices could be used to track Stingray activity, though given the ever-changing world of security and privacy, something like this could only be effective for so long!