Thieves may soon have to learn how to imitate walking styles if they hope to steal expensive handsets and notebooks.

New technology developed by Finnish scientists detects changes in the owner's physical movements and locks the device if it senses anything unusual, the VTT Technical Research Center said.

Sensors installed in the device measure certain characteristics of a user's gait, which are then stored in the device's memory. The sensors continuously measure that gait and compare this data with the stored values. Should the values differ, the device automatically freezes and can only be reactivated with a password.

"One of the main advantages of this biometric method is that it is unobtrusive and requires no special action on the part of users," said research director Heikki Ailisto.

Compared with passwords and other biometric methods of identification, VTT's technology confirms identity as a background process without any need for user intervention. The researchers tested the technology over a two-month period on 36 people, of whom 19 were male and 17 female. The identification rate was over 90 percent, they said.

But the new technology is not without its challenges, according to Ailisto. It must learn to deal with users who have different walking styles, caused by choice of shoes, among other things. For another, it requires sensors that are still not widely available, and so are pricey.

Despite the challenges, Ailisto expects the patented technology to find its way into new mobile phones, PDAs and notebooks over the next two years.