You are massively overthinking the problem. The very first system of this type I saw didnt even have a microcontroller. Just an eprom for driving LED array, bun

You are massively overthinking the problem. The very first system of this type I saw didnt even have a microcontroller. Just an eprom for driving LED array, bunch of TTL logic and two inputs. One linked with 'open doors' switch, the other going to undo switch. And it worked fine for couple of years in a >million city.