It's a real problem, but I don't know if your idea would actually solve anything.

I think the biggest risk for this is when there's a change of routine like when mom gets sick and dad is supposed to take the little one to daycare. So if mom has the special keychain and dad doesn't, it won't work.

Many men (myself included) keep their keys in their pocket, so I try to keep my keychain to a minimum. I hate the big plastic keys and I don't need or use the radio remote door locker. So maybe I wouldn't put your thingy in my pocket either.

Also, now you'll need batteries or a charger for the beeper and the blanket. What a pain.

I think when we put babies in the front seat, it was a better solution and they could see you while you drive. I hate it that kids are in rear facing seats in the back seat and you can't see them or they you. And when they spit-up or choke on a bottle, the alternatives are to pull over and get out and get to the back seat, or just let them cough-it out. Also bad when they're crying. I think these risks are worse than the safety an air-bag provides for other passengers, which is I believe the reason kids are relegated to the back seat now.