If I was building a new wash, I might put a loop in the floor so at least once the meter stopped, it could keep beeping until they put money or or pull out. Maybe even a voice recording, "your wash has ended, please exit or deposit additional payment". If I was tech savy I would have it say welcome to our wash on entry and then if no payment ins 3 minutes, go to the exit message and beeper.... But then I don't even run off teh bucket washers, just glad they spend some money, get lots of free car wash cleaning spray bottles usually at least half full too... to bad I no longer wash my car at home.