Minecraft wiki entry for Combination_locks, associated text: Make a series of buttons, and connect only one to an RS NOR latch. Then connect both the RS NOR latch and a second button to an AND gate, which feeds to another RS NOR latch. Do this continually until you have either filled all of the buttons or are satisfied with the lock. Connect the final RS NOR latch to a separate AND gate with a signal from an enter button. Feed that to the output RS NOR latch. Then connect any of the left-over buttons to the enter button and send reset signals to all of the RS NOR latches. A pressure plate next to a door can reset the door. This type of lock has severe limitations its security. For example, not all the buttons could be used in the pin or there would be nothing to reset the system.