Police are warning drivers and urging additional victims to come forward after a series of thefts from cars.
Officers are concerned by a spate of recent thefts from unlocked vehicles in Mansfield Woodhouse and Forest Town.
Items including cash, sunglasses and headphones have been taken in more than 30 incidents since 1 December.
Drivers are being urged to double-check their car doors are locked, and also to make police aware of any recent incidents involving their vehicles.
Sergeant Kate Long, of the Mansfield North neighbourhood policing team, said: “These are opportunist crimes where offenders have repeatedly tried car door handles until they find one that has been left unlocked.
“We are working hard to identify the people or person responsibly but have also decided to issue a public warning to all vehicle owners in these areas.
“We also want to hear from any other victims who have not yet contacted us. We know that some people don’t report these kinds of offences.
“That may be because of the limited value of the items stolen, or a level of embarrassment at having left their vehicles unlocked.
“It is vital, however, that people know the location of all offences of this type so we can identify any additional patterns to this offending and bring all those responsible to justice.
“Leaving your car unlocked is an easy mistake to make. Most of us have very busy lives and I have even done this myself. By taking a few moments to double check we can all remove potential targets from local criminals.”
Anyone who has had their car broken into is asked to call police on 101.