Observer

Observers are blocks that emits a redstone signal when an adjacent block is updated.

Breaking
An observer requires a pickaxe to be mined. When mined without a pickaxe, it will drop nothing.

Placing
An observer is placed similarly to a log, and will observe the block that it is placed against.

Behavior
An observer will detect changes in its target's block ID or data value, or the breaking or placing of a block. When it detects something, the observer emits a 1-tick (2 game ticks) redstone pulse from its opposite end.

Observers can detect a wider range of phenomena than a block update detector (BUD) circuit in the computer edition can detect, though has different limitations.

Observers will not detect:


 * Powering / depowering of activator rails
 * Inverting / deinverting a daylight sensor
 * Activation of a dropper or dispenser
 * Natural growth of grass, or decay of grass into dirt due to lack of light