Thieves are getting easy pickings in Long Sutton and Sutton Bridge because drivers are failing to lock their cars.
Police say there was an increase in thefts from cars in the Suttons during May, but most of the crimes involved unlocked cars.
A Lincolnshire Police spokesman said: “Over half of the reported incidents involved vehicles which were unlocked at the time of the crime and motorists are urged not to let themselves become an easy target for thieves.
“Items including sat navs and loose change were stolen.”
Police say drivers should always lock their cars when they park up, even if their vehicles are tucked away in garages or left on their own driveways.
At other times, drivers are advised to park in well-lit areas where their vehicle can be seen by passers-by at night.
And everything and anything of value should be removed from the car.
A police spokesman said: “Never leave anything on display in your vehicle. Even small change could pose an attractive target for opportunist thieves.”
Sat navs are a prime target and police say drivers should remove them, their cradle and suction pads from the car – and even wipe away marks left on windscreens by the suction pads.