Drivers are being warned not to leave satellite navigation systems in their vehicles after a sharp rise in thefts.
Sat-navs were one of the most popular gifts at Christmas
Up to 250,000 systems were stolen last year in the UK, estimates suggest.
Police have long warned that a sat-nav cradle on a dashboard or the suction cup markings can indicate there may be one of the gadgets hidden somewhere.
But they say thieves are now using hi-tech tracking technology to enable them to find out whether a device is kept out of view.
Officers advise motorists to take the systems with them when they leave their vehicles.
Sat-navs, which help drivers find the correct routes, were among the most popular gifts at Christmas.