DENVER — Aurora police Sgt. Dan Mark saw the lights on first, then the exhaust puffing from the tailpipe.
The Lincoln Navigator was running, the keys locked inside. Nobody was around.
"If an individual wants to steal a car, all they have to do is hang out around the corner," Mark said.
"It takes literally just a couple of seconds to run over, jump in the car and take off."
Every year, when the cold weather kicks in, police see a spike in people who start their cars to warm them up and then walk away.
That means it's the busy season for car thieves waiting for the perfect opportunity to just hop in and drive.
"I realize it's inconvenient to sit while your car is warming up or drive while your car is warming up, but it's not as inconvenient as having your car stolen," Mark said.
"I tell people it's a lot colder when you're standing outside your driveway or outside the 7-Eleven when you realize that your car's gone."
Across the Front Range, police have been out en masse this week, looking for "puffers," writing tickets and educating motorists.
Leaving a vehicle running and unattended is against the law in Colorado.
Mark tells this to Karina Patton when she comes back outside, to her Navigator.
"Really?" said Patton, who recently moved to Colorado from California. "I'm glad you told me because I sure didn't know."
The ticket: $75
Patton had turned on the vehicle to warm it up.
Then she dashed back inside her home to get her 9-month-old daughter settled in with grandma for the day.
Now, the ticket will cost Patton about $75. She started to cry.
"I just started doing that this week," she said. "I wasn't even inside for three minutes."
Last year, 13,010 vehicles were stolen in Colorado, and thieves attempted to take an additional 1,229. Colorado doesn't track puffer thefts, but cities across the country that do estimate that 10 percent to 50 percent of auto thefts occur because keys are left in the vehicle.
In Aurora, there have been more than 650 puffer thefts since 2004, when the police department began tracking them. An average of nearly two dozen puffer vehicles a month are stolen in the cold-weather months of December, January and February.
"A lot of people just don't think. 'Well, nobody would steal my car. It's out in front of my house,' " said Colorado State Patrol Investigator Billy Mayfield. "Well, that's exactly where they're out looking. They're driving the neighborhoods."
And this time of year it's easy pickings for even the most amateur thieves.
Think of it as an open invitation to steal your car.
"These are easy," Mayfield said. "You don't have to get in and break anything. You don't have to defeat any security system. You just get in and drive it."
In Douglas County, deputies have found 164 "puffers" this week, many left unattended in driveways or on residential streets, said Detective Cesar Madrigal.
All but one of the drivers received a warning.
"Your car could have just been stolen," read the informational pamphlet left on each vehicle. Deputies also have given out 13 steering-wheel locks."I know I dread it in the morning, sitting my rear on that cold seat and waiting for it to warm up," Madrigal said."It is inconvenient, but it has to be done."
Back in Aurora, Mark pulled up behind a station wagon.
Seconds later, Amanda McKenzie came outside. She said she was getting ready to take her aunt to chemotherapy, and she was "pretty upset" that Mark was writing her a ticket."My aunt is almost 80 years old.
She's dying of cancer," McKenzie said. "She can't very well get into a cold car."
Luis Martinez doesn't want to sit in a cold car either.
But when Mark found Martinez's Jeep running unattended outside the man's home, Martinez didn't get a ticket. That's because he had a remote starter and a kill switch to prevent the Jeep from being driven without a key in the ignition.
"I already had my stuff broken into. It's too much of a headache," Martinez said. "I'd rather be smart about it."