Mobile phone tracking technology is being put to good use watching how punters migrate around a shopping centre, thanks to gear from Portsmouth-based Path Technologies.

By installing receivers around a shopping centre the company can pick up communication between handsets and base stations, enabling them to track shoppers to within a metre or two - enough to spot the order in which shops are visited. Two UK shopping centres are already using the tech, with three more deploying in the next few months.

This information is used to work out if shoppers are dropping in to visit one particular store, or doing the rounds of 15 different shoe shops before going back to buy the first pair seen. Retailers will pay good money for this kind of data, but while existing solutions are based on counting heads or asking questions of a selected few, watching where the phones go is far more useful.

Most of the GSM connection is encrypted, so there's little chance of an individual customer being identified. Even the IMSI (International Mobile Subscriber Identity – the user's phone number) isn't normally sent over the air; the network issues a TMSI (Temporary Mobile Subscriber Identity) which is only valid until the next authentication.

A TMSI is like a dynamic IP address, so punters can be tracked as they move around the centre. But if you want to drop off the radar, you can just reset your phone - you'll get a different TMSI to confuse the software with.

Path Intelligence is very keen to distance itself from those privacy-invading companies that track your online existence then claim it's all anonymised. Path will track your real existence, but point out they can't establish who you really are or follow your phone after a reset even if they wanted to.

The company does point out how broadly the concept can be applied. Once one assumes that each person is carrying one mobile phone (a statistically realistic assumption in Europe), then you can track everything from cars driving around a city to how far people will walk across a stadium to get a hotdog.

Trade shows are an obvious application. Knowing how long a visitor spends at each stand is very valuable. The company recently did trials at O'Reilly's Web 2.0 conference where the popularity of iPhones meant there was enough GSM technology to gather some useful statistics. For the moment Path Intelligence only does 2G GSM, though supporting CDMA wouldn't be too difficult. 3G GSM is slightly more secure but still uses a TMSI, so those on a 3G network are unlikely to remain untracked for long.

Whether punters will be happy about being tracked anonymously remains to be seen. Path Intelligence points out that it has less information than the network operators, but you might trust your network operator more than the company running the local shopping centre. And while the tracking is anonymous, it wouldn't take a genius to match a tracked phone to a CCTV recording and fill in the gaps for one visit at least. ®