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AURORA, Colo. — It can be tempting to warm up your car on cold days like Tuesday morning. But you would be breaking the law if you did.

Dozens of people learned that the hard way in Aurora as officers executed a city-wide “puffer” operation Tuesday morning. Warming up your car could leave you out in the cold.

“It invites crime. It invites a thief to steal your vehicle,” Aurora police Officer Patricia Perea said.

It’s why she was one of 30 officers on puffer patrol, seeking vehicles left running unattended. The steamy exhaust is a tell-tale sign that car thieves target and creates problems not only for drivers but police and the community.

“Thieves like to steal other people’s cars to commit crimes,” Perea said.

She hit a hot streak spotting the cold cars. And when she couldn’t track down one driver, she took the keys.

“You saw today how easy is it to take a vehicle that’s running. I took keys out of car that was not attended and no one even saw me,” she said.

The penalty for puffing is a ticket. The fine is determined by the courts. Even one driver, who had his car doors locked but the keys in the ignition, won’t be spared.

“I have a spare key. But they could still break a window and get in it,” said the driver, who did not want to be identified.

During the operation, the officer came across another vehicle that looked like a puffer. But it wasn’t because the owner started remotely, had the keys and the doors were locked.

Police said if someone puts a remote-started car in gear it kills the engine.

“They won’t be able to get away with the car,” Perea said.

The 10-year veteran said drivers will thank her that they’re keeping an eye on their cars. But sometimes she has to remind them it’s better to get a ticket than a thief take their vehicle.

“It’s just not worth it. Don’t start your car to be a little warmer,” she said.

The warmth the sun naturally provides means the end of the puffer patrol — but with a message that’s never exhausted.

Aurora police did not have a total tally of the tickets its officers issued Tuesday morning. The department said Aurora saw a 16.7 percent increase in motor vehicle thefts from 2014 to 2015, from 965 to 1,126 thefts.