Minecraft wiki entry for Telegraph, associated text: Although they are similar to buttons in their general impracticality, the player could potentially utilize the pressure plate's unique ability to be activated by mobs. Multiple pressure plates could be positioned at different points of a cave, all of which could be connected to the one-way distress telegraph mentioned earlier. If any mob (only harmful mobs would spawn in a deep cave) stepped on one, it would trigger the distress signal, and players elsewhere would be alerted and be able to take action.