This is a project which I’ve been following for a while, and it serves a worthwhile purpose. Already, most people who are security-conscious will already be actively managing their phone’s data connections, using VPNs or tor, data/transmission encryption and being very selective with app permissions, this is all a given. However, the easiest method to gain access or track individual phone’s is via the mobile base station, or cell tower which it’s constantly connected to.
There are commercially available ‘fake’ cell-towers which individuals can buy, and industrial-strength versions are widely deployed by governments and law-enforcement agencies worldwide (the FAQ on the linked page has more information). Since most phones will mindlessly jump between whichever cell tower is convenient if it passes the most basic of tests, it’s straightforward to set up a MITM attack on devices, at which point the possibilities are endless. You can be certain that multitudes of these will be rolled out to public gatherings, busy areas, inside corporate premises, etc, if they are aren’t already.
How Android IMSI Catcher Detector works (and it’s distant cousin SnoopSnitch) is by comparing data from currently connected cell towers against a known repository of crowdsourced cell towers. If cell-tower position, signal strength or ID abnormally changes over a fixed time period, something is awry. Often these fake-base stations (known as Stingrays) will force devices to boost their transmission signal to make interception easier – this is a GSM function that phones have no control over. Of course, this is not a foolproof, but security is a layered approach.
Root required, and Android only.
“In the USA the IMSI-Catcher technology is known under the name “StingRay“, often mounted out of sight on top of cars. The FBI or local police regularly deploys IMSI-Catchers hidden in vehicles at a protest to obtain a record of everyone who attended with a cell phone (leave your phones at home by all means if you really have to attend). IMSI-Catchers also allow adversaries to intercept your conversations, text messages, and data. Police can use them to determine your location, or to find out who is in a given geographic area at what time. Identity thieves can use freely available tools to monitor GSM communications from a parked car in your residential neighborhood, stealing passwords or credit card information from people nearby who make purchases on their phones.”