Scarborough Police are urging residents to remove valuables from their vehicles and double check that they are locked when not in use.
Officers have issued the warning following a number of thefts in the town from four unlocked cars in just one night.
Opportunist thieves simply opened the doors to the unlocked cars and helped themselves to what was inside, overnight on April 2.
Stolen items include a designer coat, sunglasses, handbag, cash, keys to another car, Argos parcels and children’s toys.
In one incident the spare key to the car was found inside the car and the suspect drove off in it. It has since been recovered.
A man and a woman have been arrested in connection with the investigation. They have been released on conditional bail while the investigation continues.