On Tuesday alone, New Castle County police say five cars were stolen this way.
Elise Taylor warmed up her car and ran back inside the house for a few minutes. Seconds later, her car was gone.
"I went out clearing off snow off my car and I turned on my car to warm it up to get off the ice off the windshield. I came back inside for three minutes. I thought I heard noises and I looked out and the car was gone."
In New Castle County, of the 71 stolen cars so far this year, 25 of them were unlocked, with keys in the ignition and the cars were running.
In Wilmington, police say 80 percent of the vehicles stolen in the first week of February also had the keys in them.