Minecraft wiki entry for Defense, associated text: Place pressure plates around an area you would like to protect, or your entrance(s); try to keep them separated as much as possible (optional). Then, attach the note block(s) to the pressure plates with redstone wire. From now on, whenever a mob or a player walks on a pressure plate, the note blocks will generate a sound notifying you. If you mine often, put a note block(s) in your mine or along a rail road.