I've never left one in a car, but I "almost" did once. Remembered it, when I got to the front door. My littlest was about a year old. 99 times out of 100, my wife would pick her up after work. One evening, I had to. She was asleep in a car seat, in the back seat of my truck. I came in from work, and headed in the house to change clothes, and start my afternoon on the farm. Scared me to death, when I realized what I had done. I'll admit, it was probably less than 30 seconds, but it made me see how easily somebody could do it.