 God forbid they get out of the car, right? They have sensors. Some you have to put in professionally, and some are only compatible with certain car seat brands. But just don't forget these little kids shouldn't even be in a car too long. Make sure there's AC. Make sure there's air. They have crib and mattress toppers, I was reading, that would have built-in cooling now, too. You might want to look into that.