According to recent research funded by the EU and the German government, and reported in The New Scientist, mobile phones give off a unique set of variations within their radio signal which has the potential to be employed by law enforcement to track any handset.

Though the initial research carried out at the Technical University of Dresden represents a small sample of 2G handsets, the science behind the theory is solid. The radio hardware in your mobile phone consists of a mix of components including power amplifiers, oscillators and signal mixers that can all introduce radio signal inaccuracies depending on the quality of the individual component. By introducing time-based patterns of modulation, and carefully removing random effects of the wireless communication channel, these errors can be distinguished as a unique device-dependent feature.

When analogue signals are converted into digital phone signals, the stream of data each phone broadcasts to the local mast contains these unique error patterns giving the handset it distinct digital ‘fingerprint’.  The University researchers believe this can be used for digital forensics, to identify and track mobile phones operating on a GSM network. By implementing specialised receiver software, the team believes it can enable law enforcement to passively monitor GSM traffic, identifying mobile phones at an overall success rate of 97.62% under real world conditions.

Because the technique is passive, with nothing sent to the handset, it cannot be detected by criminals who currently try to evade handset tracking by altering a mobile’s built-in ID code or by regularly swapping over SIM cards.

The researchers recognise that this just the first step in mobile forensics to identify mobile devices on a GSM network without relying on traditional identifiers like IMEI or IMSI.

You can read more about the Technical University of Dresden’s research here.