An IMSI catcher is an illicit mobile phone base station designed to intercept the traffic from nearby mobile phones by persuading them to connect to it rather than the real phone company tower. The IMSI in the name stands for International Mobile Subscriber Identity, a unique global identifier that all mobile phones have. IMSI catchers are typically used by government agencies to detect and track people at particular locations, and are thus the subject of some controversy.

As is so often the case when a piece of surveillance technology is used in a controversial manner there is a counter-effort against it. The IMSI catchers have spawned the subject of this post, an IMSI catcher detector app for Android. It’s a work-in-progress at the moment with code posted in its GitHub repository, but it is still an interesting look into this rather shadowy world.

Android IMSI-Catcher Detector
https://hackaday.io/project/3824-android-imsi-catcher-detector

An open source app to detect fake base stations (IMSI-Catcher / StingRay) as well as silent SMS in GSM/UMTS networks on your mobile phone.