Did you leave the car unlocked while it warmed up this morning? Did you let it idle while you ran in and got your morning coffee?

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These often routine habits for New Jersey drivers, especially during the colder months, are drawing a new warning from the New Jersey State Police and the New Jersey Division of Highway Traffic Safety.

New Jersey State Police Sgt. Jeffrey Flynn said leaving an idling car unattended and unlocked is a good way to fall victim to "puffer thieves," a term known among  thieves for these types of cars.

"They're easy to spot for car thieves. They see them idling in parking lots or in your driveway," Flynn said "The car is running, it's unlocked. A thief hops in and drives away."

Flynn said it's particularly easy for car thieves to spot these cars in the winter because the exhaust fumes are more visible.

Authorities are urging drivers not to let themselves fall prey to "puffer thieves" by keeping their cars locked.

For those motorists that want to warm up their cars in the driveway or keep them on while they run into a convenience store, Flynn recommended using a spare key to unlock it or to invest in a remote starter.

"We're urging people to never leave your car unlocked while running, even in your driveway," Flynn said.

Flynn said these idling cars can be spotted from a good distance away and reiterated that it just makes it easier on thieves to quickly take a warm, unlocked car.

"If your car's locked, chances are the criminal is not going to smash the windshield. They want the easy steal and not anything that's going to bring attention to themselves," Flynn said.