Minecraft wiki entry for Traps, associated text: Instead of a daylight sensor, you can also use an observer. This trap is good because it is hard to detect. If you build this above ground, it may seem somewhat out of place, so you should cover the redstone ore with carpet or build it underground. When the target walks on the redstone, it lights up, triggering the TNT. A similar trap is achieved by putting a valuable block that the player may want to mine in place of the redstone ore. When the player breaks the block, the daylight sensor activates, provided there's a light source or clear air above it.