3 ms·

While there are less of these now (possibly because of the feature described here), if you find a store with an automatic door that swings out, standing on the

While there are less of these now (possibly because of the feature described here), if you find a store with an automatic door that swings out, standing on the pad that is outside to block the door from moving is a good way to annoy your friends who are behind you and teach them about simple state machines.

jgwil2 6y ago
Another common one (at least once upon a time) is the coin-operated turnstile, which is basically (ab)* where a is inserting a coin and b is rotating.