Texas

And with todays tech, would be much easier to produce

Require all car seat manufacturers to install a proximity alarm on the seat. It works with an apt on your phone. As soon as you are 20 or more feet away from your child’s car seat,, it goes off

The alarm sensor in the seat is weight based. Remove the child, alarm shuts off

After market kits could be made for older model car seats

If I were a coder and/or had connections, I would do it myself, but alas…