Minecraft wiki entry for Quasi-connectivity, associated text: This means that when these redstone components are attached to a block beneath them, they can activate the space above a piston (one block away), and also simultaneously update the piston as well (two blocks away). A trapped chest updates redstone components adjacent to the space beneath it, but doesn't need to be attached to any block (for example, like a pressure plate) — the other examples below use an upside-down slab instead of a block because a powered block would activate the pistons directly. A tripwire hook cannot be attached to a block beneath itself so cannot be used for immediate QC activation.