Minecraft wiki entry for Redstone_components, associated text: While activated, a weighted pressure plate and its attachment block (unless attached to a fence, nether brick fence, slab, or stairs) both power adjacent redstone dust (including beneath the block), and all adjacent mechanism components (including those above or below it). They also activate all adjacent redstone comparators or redstone repeaters facing away from it, at a power level proportional to the number of entities on the weighted pressure plate.