Minecraft wiki entry for Logic, associated text: A useful feature is that an XOR (or XNOR) gate will always change its output when one of its inputs changes, hence it is useful for controlling a mechanism from multiple locations. When controls (such as levers) are combined in an XOR gate, toggling any control will toggle the XOR gate's output (like a light bulb controlled by two light switches — players can flip either one to turn the light on or off, or either of which can always open or close a door, or turn some other device on or off.