CHICAGO (CBS) – CBS 2 this week introduced you to a man who applies the Denver boot to his own car to prevent it from getting stolen.

Reporter Chris Martinez talked with some people who do the opposite – an unwise choice that many of us make every day.

Two Chicago sisters who normally leave their cars idling so the vehicles can warm up had them stolen Friday morning.

“I do it day after day because I don’t want to be cold,” says one of the women, Sharon.

But what happened is a wake-up call.

The two cars were unlocked with the keys inside. They were quietly driven away in less than two minutes.

One of the stolen cars is a 2012 Hyundai Elantra; the other, a Volvo S-60, about seven years old.

If Sharon ever gets her car back, she says she’ll never leave it out of her sight.

“Lesson learned,” she says.

Technically, it’s illegal to leave a car running unattended in Illinois. Police say they advise against it not just because you can get a ticket, but mostly because it’s an open invite for someone to steal your ride.