Speed trap detection equipment and other similar devices are the latest "must steal" items for opportunist thieves, police say.
Over a three-week period from 3 to 24 January, eight cars in Droitwich and Worcester were targeted for their laser and radar devices.
Motorists are being urged to make the items, which are plugged into a cigarette lighter, more secure.
Police say the thefts could have been avoided if they had been out of sight.
West Mercia Police say the majority of devices are from two ranges produced and marketed by the same manufacturer.
When the manufacturer is notified of a stolen item, it can block the signal, rendering it useless.