It might not hurt your car to let it warm up in the driveway while you sit in the house.
But it could get you a traffic citation.
"It's illegal. You can't leave a vehicle unattended with the keys in the ignition," said Sgt. Susan Hadl, a spokeswoman for the Lawrence Police Department.
She cited Section 107 of the Standard Traffic ordinance: "No person driving or in charge of a motor vehicle shall permit it to stand unattended without first stopping the engine, locking the ignition, removing the key from the ignition and effectively setting the brake thereon, and, when standing upon any grade, turning the front wheels to the curb or side of the highway."
She said the ordinance applies to vehicles on public or private property, including parking lots and driveways.
"You just can't plain leave your vehicle running with the key in the ignition," she said. "That is not to say that we rigorously go about enforcing that every day."
Hadl wasn't sure how the law might apply to new devices that allow you to start your car by remote control from your house.