Minecraft wiki entry for Redstone_components, associated text: A pressure plate turns ON when an entity (mob, item, etc.) crosses or falls on it, and turns OFF when the entity leaves or is removed. A wooden pressure plate may be turned ON also by falling items and arrow shots. A wooden pressure plate that is activated in this way turns OFF when the object is picked up or despawns (after one minute for a shot arrow, or up to five minutes for an item).