> Many would answer as high as 95%, but the correct probability is about 2%.
Your system would be orders of magnitude less effective than you are imagining. It's a common enough mistake that it has its own example on that wikipedia page.
You really want to mandate a system where something like 98% of the calls to police would be false positives? Who will pay for all these extra officers who do nothing but drive around the city freeing innocent, sober people from their cars all day?
The seat belt situation is fine, because:
1. Your car doesn't refuse to drive if you don't wear one (such as on private property where it's legal to drive, drunk, with no seatbelt, if you choose)
2. Your car won't hold you hostage for hours if some AI algorithm makes a mistake. The seatbeat detector is 100% accurate under normal conditions and if it fails, the worst thing that can happen is your car will beep at you.