Researchers at the University of Washington uses a sensor box, including a GPS module, a GSM cellular modem, a Raspberry Pi, a cellular hotspot, and an Android phone running SnoopSnitch, to collect 2G cells information and detect IMSI catchers, as you can read in the wired.com article.

They identified and mapped out 1,400 cell towers in Seattle, and 700 in Milwaukee, finding anomalies in the Seattle area.

More information can be found in the project web page and their  white-paper.