Oops. I was really thinking about parking zones with a time limit and no meter. (What's the right term? "Parking enforcement officer"?) You could make a case for a timer app with a loud alarm.
(If they patrol a 2-hour zone once every 2 hours, you get 2-4 hours; average 3. On bad advice the other day I moved the car down the block at 2 hours, and later did a web search and learned one has to move the car to another block, and did that. Not sure if one can move back to the first block 2 hours later. I suspect nobody was patrolling.)