WHEAT RIDGE, Colo. (CBS4) – It’s called “puffing” — vehicles left running to warm up on cold days. After a rash of thefts, police are urging people not to do it.

A cold winter day brings snow, ice, frozen windshields and a chilly car ride. That makes puffing that much more tempting.

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“It’s when people go outside and start their cars to warm them up and then go back in their houses,” driver Marlene Elenbaas said.

In Wheat Ridge the police department has seen a series of vehicle thefts lately — nearly a half a dozen this week. All the stolen vehicles were puffers.

“Just this morning we had another one stolen from an area just behind the police department,” John Romero with Wheat Ridge police said.

Police say it happens all over the metro area and call it a crime of opportunity.

“Unfortunately what we see with these puffers is that they’re stolen,” Romero said.

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It’s also a crime that can earn a citation.

“Any time your car is running unattended it could slip into a gear. There are just a ton of things that could happen when you’re not in your car and it’s running,” Romero said.

Police add it is legal to leave a vehicle running and unattended only with a remote starting system.

“My car is a newer car, so it locks,” Elenbaas said.

Right now crews are just handing out warnings in an effort to protect citizens and catch criminals.

“We would rather just have people know the dangers of what they are doing rather than have them call us when their car is stolen,” Romero said.

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The Metropolitan Auto Theft Task Force will be conducting puffer enforcement to crack down on thefts. Police in Aurora and Denver plan to ticket drivers.