LAKEWOOD, Colo. (WPVI) -- Most of us want to spend as little time as possible outdoors on these brutally cold winter days, and many drivers warm up their cars before getting in it.
But police warn that is a tempting target for thieves.
Car thieves were recently caught on surveillance rolling up on an idling car in Denver and seeing it's empty before stealing it moments later.
In another incident, a thief scouts a car, parks, approaches and then darts to open the door, but it's locked. In this case,the homeowner sees what's going on and scares the thief away.
In a parking lot, surveillance also caught a thief casually walking, then speed up to get in a car. The driver comes out in time to try to stop him, but it's too late.
Many drivers leave their cars running to warm up on cold mornings.
Cops call them "puffers" but bad guys call them a golden opportunity.
And police departments across the country are again warning drivers not to leave their running cars unattended.
Less than 60 seconds is all it took to steal Gregory Kehrl's car. If that's not bad enough, the thieves also got away with keys to his second car, which were inside. Later that night they came back to steal that one, too.
You may not realize that in many states, it is illegal to leave a car idling with the keys inside. And depending on your state and county, that could even mean it's even illegal in your own driveway.
But more people seem to be doing it. According to the National Insurance Crime Bureau, more than 57,000 cars stolen in 2015 had keys inside.
In Lakewood Colorado, ABC News hit the streets in January with Sgt. Dave Hoover. Within minutes his officers spot dozens of puffers idling in the 18-degree weather in front of homes and stores.
One driver was hit with a $57 dollar ticket. Not far away, Rick Boyer's car has just been stolen.
"It's cold out. The windows are frosty so I warm the car up and go back inside. I'm in there maybe 3-4 minutes and come outside to see the car is gone," he said.
Police say stolen puffers can cause a crime ripple effect beyond the owners.
"We've seen them used in drive-by shootings and burglary cases. We've even had instances of bank robberies where the suspects were stealing puffers as a means of getting to and from the scene," said Lakewood Police Chief, Kavin Paletta.
On a cold day, Sgt. Hoover says a little shivering is better than a lot of stealing.
"Sit in your car," he said. "That's what they made gloves for."