Stamford police are warning residents of a recent increase in thefts of expensive car Global Positioning System (GPS) units.

Police believe the thefts are occurring for three reasons. They say the GPS units are in high demand, expensive and relatively easy to steal because people put them on their dashboards or mount them on their windshield.

Stamford police say the number of GPS units stolen in August so far is triple what it was last year.

Officer Peter di Spagna says drivers must still be cautious even if they lock their cars. He says even if drivers take their GPS units out of their cars, leaving the holders in the car could still invite a break-in.

Police advise people with GPS units to record the serial number because it?s the only way to help track it down if it?s stolen.