They have a shutoff on the right hand side of them, as you are looking at it, where it takes a 90 degree turn as it comes out of the wall. All it takes is a flat screw driver and you can shut the water off. Sometimes they might have a vandal proof cap, but you can just take the screw driver and pry the edge and pop it off, and when your done just pop it back on. Just be careful, sometimes they can leak, or will constantly run (I won't get into those details on how to fix).
BTW I'm in commercial / industrial plumbing and HVACR
The one above has a manual flush button which is right above the sensor.