Useless Invention # 453

According to the AP:

"Devices exist to keep kids from dying in cars, but few are sold
Your car has a sensor that tells you when you've left the headlights on or the keys in the ignition. It probably has another reminding you and your passengers to buckle your seat belts, and still another that sounds when the door is ajar. Some cars even to tell you when the tires need inflating. But so far, there's no standard equipment to tell you that you've left a child in the back seat of a hot car."

Because it's okay to leave your child unattended in a cool, comfortable car while you get your nails done.