Redstone · Mechanic · Java & Bedrock
How to Use an Observer
An observer is a block-change detector. It stares at whatever is in front of its face, and the instant that block changes it fires a quick pulse out the back. That single trick runs most auto-farms and flying machines.
watched block
WATCHING…CHANGE → PULSE!
An observer stares at the block in front of it. The moment that block changes, it fires a quick pulse out the back. That is what makes crops auto-harvest the instant they grow.
What it detects
Any change to the block it faces, never items or mobs.
Crops & saplings growing
Pistons extending or pulling
Redstone power changing
Water or lava flowing in
Levers, doors, trapdoors
Even another observerFront watches, back fires
The big staring face is the detector, pointed at the block you watch. The back with the dot is the output. Get them backwards and nothing fires, so always aim the face at the block and pull redstone from behind.
Quick answers
What does an observer do?
It watches the single block directly in front of its face. The moment that block changes in any way, it sends a short redstone pulse, about one redstone tick, out of its back.
Which side of an observer outputs the signal?
The back, the face with the small dot. The big staring face is the side that watches. Place the face toward the block you want to monitor and take the pulse from the opposite side.
What can an observer detect?
Block changes only: crops and saplings growing, pistons moving, redstone dust or levers or doors changing state, water and lava starting to flow, leaves decaying, and more. It does not detect items lying around or mobs walking past.
How do you make an observer clock?
Point two observers at each other, or an observer at its own output. Each one keeps detecting the other's change, which makes a very fast 2-tick clock. Use it sparingly because fast observer clocks cause lag.
Why is my observer not detecting anything?
Check the facing. The staring face has to point at the block you are watching, not away from it. Also remember it only fires on a real block-state change, so items or mobs passing by will not trigger it.
Do observers work the same on Bedrock?
Yes. The watching face and the pulse output behave the same on Java and Bedrock, so the same auto-farm and flying-machine designs work on both.