This page describes a circuit for controlling access through a door. The circuit will lock the door after the character enters it the first time. The door remains locked until the unlock switch is found and activated. This is a one-time circuit. Once it's activated, it can't be undone. There's really no point to it once the player finds the unlock switch, anyway. The Reset input on the SR can have a button installed to reset it when you are testing the operation. An example of this circuit can be found in the Circuit Cookbook world by Stanimus .