More cars were stolen in Denver last February than any other month.

It’s tempting to warm up your car a bit before you get inside and head out to embark on a chilly Colorado day (like today).

But as Denver police will warn you, too often, people do this and then leave their cars unattended. They call them “puffers” and you can get a ticket for doing that. Or your car can end up stolen. And data from last year suggests this month is the most popular month for stealing puffers.

Puffers were stolen 473 times last year, according to department data. February was the busiest month for car thieves, with 102 puffers stolen. September had the lowest number, with 4.

Between Jan. 1 to Jan. 28 of this year, 47 puffers were stolen, according to department data.

Denver police usually try to warn people about leaving cars unattended through tweets (and gifs). But as department spokesman Doug Schepman said an email, officers also like to conduct proactive patrols around the city to look out for puffers. Their goal is to prevent your car from getting stolen.

State law prohibits you from keeping a car unattended after turning it on and leaving it on public property (like streets). You can get a ticket for doing that, and you can also get a ticket if you keep it idle for longer than five minutes (even if you’re in the car!) on public or private property. A ticket for an unattended car can cost you up to $100, while an idling infraction can result in a max fine of $999 and up to one year in jail.

There are some exemptions to this idling law if temperatures drop below a certain temperature; for example, the law doesn’t apply if the temperature has been below 20 degrees Fahrenheit for the last 24 hours.

“While a citation is possible, officers typically contact the owner of the ‘puffer’ and educate them regarding the law and the increased risk of auto theft when leaving a running vehicle unattended,” Schepman said in an email to Denverite. “Our recommendation for vehicles without remote start is for owners/drivers to remain with their vehicle while it warms up since the theft of one’s car is far more inconvenient and impactful on their daily lives than being cold or uncomfortable for a while.”

Cars with a remote start are exempt from the unattended law to some extent, but if its longer than five minutes, they can get ticketed as well.