I was at a hotel once and went to the bathroom while heating up some food. The microwave finished and beeped like 10 times then beeped every 15 seconds until I opened the door. I don't really understand what problem that's meant to fix, it's not like the microwave keeps microwaving after it beeps and shuts off, nothing's going to catch on fire

My drier at home does this too, although every 10 minutes as opposed to seconds, and I don't understand that either. Washing machine I could understand since if you forget about it for too long it might go mildew-y, but once my drier is done, it's done, and won't turn back on until Its turned back on. A beep every 10 mins might be nice as an optional toggle or something for forgetful people, but it's just plain annoying