Observer
Observer fires a one-tick pulse whenever the block in front of it changes — an indispensable trigger for compact farms and machines.
Description
This simple behaviour makes it the most important automation primitive in modern Minecraft engineering. Wired with pistons, observers form flying machines and tile-based pulse extenders. Watching crops, they trigger automatic harvesters. Watching a daylight cycle change, they activate dawn-dusk lighting. Compact, predictable, and deterministic, the device replaced sprawling clock circuits as the standard trigger source. Crucially, observers do not detect entity movement — only block-state changes — which keeps their behaviour reliable across high-load servers.
Java & Bedrock Guide
How to use an Observer in Minecraft
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1
Craft the observer
Place 3 cobblestone across the top row, then redstone dust, redstone dust and nether quartz across the middle row, and 3 cobblestone across the bottom row to craft one observer.
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2
Aim the face at the target
Place the observer so its eye-like front face points at the block you want to monitor. The face is what watches; the side with the small arrow is the output.
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3
Read the pulse from the back
When the watched block changes state, the observer emits a 2-game-tick redstone pulse from its back. Wire that side to pistons, dispensers, droppers or a redstone lamp.
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4
Build the automation
Chain observers with sticky pistons for flying machines, point one at crops for an auto-harvester, or face two observers together to make a fast pulse clock.
Observers detect block-state changes only — not entity movement. Sneak while placing to control orientation, and remember the output comes from the side opposite the face.
How to craft this block
Related blocks
Frequently asked questions
How do you craft an Observer?
Combine 6 cobblestone, 2 redstone dust and 1 nether quartz in a crafting table — 3 cobblestone on top, redstone, redstone and quartz in the middle, 3 cobblestone on the bottom — to make one observer.
What does an Observer detect?
It detects block-state changes in the single block its face points at, such as a crop growing, a piston extending or water filling a square. It ignores passing mobs and players.
Which side of the Observer outputs the signal?
The signal comes out of the back, opposite the eye-like face. A small redstone arrow marks the output side.
How long is the Observer pulse?
In Java Edition the observer outputs a redstone pulse lasting two game ticks (one redstone tick) each time the watched block changes state.
What version added the Observer?
The observer was added in Java Edition 1.11 and Bedrock Edition 1.0.
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