OBSERVER
Detects block state changes in front of its face and emits a 1-tick pulse from its back. Detects placement, removal, growth, state changes, and more.
Crafting Recipe
6 Cobblestone + 2 Redstone Dust + 1 Nether Quartz → 1 Observer
Signal Behavior
Input
InputBlock state change in front of face
Output
Output1-tick pulse (signal 15) from back
Max Signal Strength
Max Signal Strength15
Delay
Delay2 game ticks (1 redstone tick) pulse
Modes
- Pulse on block update detection
Overview: what the Observer is and does
Detects block state changes in front of its face and emits a 1-tick pulse from its back. Detects placement, removal, growth, state changes, and more.
As a trigger it watches the world for an event and converts that event into a redstone signal. It is the block-update sensor that powers crop-growth detection, BUD switches, and the cycle of every flying machine.
The Observer was added to Minecraft in 1.11 and everything described here reflects its behaviour in Java Edition 1.21.
How it works: the redstone mechanics
On the input side, block state change in front of face. On the output side, 1-tick pulse (signal 15) from back.
It watches the single block directly in front of its face and emits a 1-redstone-tick (2-game-tick) pulse of signal 15 from its back whenever that block changes state — placed, broken, grown, powered, and so on. It reads only that one front block, never its sides.
Its output is a pulse, not a held signal: 2 game ticks (1 redstone tick) pulse.
It can output a maximum signal strength of 15, which travels 15 blocks through bare redstone dust before fading to nothing.
It operates in the following modes: pulse on block update detection.
How to set it up
- 1Craft the Observer: 6 Cobblestone + 2 Redstone Dust + 1 Nether Quartz → 1 Observer.
- 2Decide where the signal needs to start or land, then place the Observer against a solid surface so it can see the event you want to detect.
- 3Lead the signal it produces into a repeater or dust line so the rest of your contraption can respond to the detected event.
- 4Test in a creative-mode plot first: trigger the input and confirm the Observer behaves exactly as the timing above predicts before committing it to a survival build.
Uses & applications
- ▸Block update detection
- ▸Crop growth detection
- ▸Sugarcane/bamboo farms
- ▸BUD switches
- ▸Flying machines
Tips & common mistakes
- !Only detects block in front of face, not adjacent
- !Emits from back, not the detecting face
- !1-tick pulse is very short, may need extension
- !The output comes from the back face, not the watching face, and the pulse is just 1 tick long, so you often need a repeater to stretch it.
Observer FAQ
What is the Observer used for in Minecraft redstone?
The Observer is most often used for block update detection, crop growth detection, sugarcane/bamboo farms, and BUD switches. As a trigger it watches the world for an event and converts that event into a redstone signal.
What signal strength does the Observer output?
1-tick pulse (signal 15) from back. Its maximum signal strength is 15.
How do you craft the Observer?
6 Cobblestone + 2 Redstone Dust + 1 Nether Quartz → 1 Observer. It was introduced in 1.11.
How long is the Observer's pulse?
2 game ticks (1 redstone tick) pulse. Because it is a pulse rather than a held signal, use an extender if you need the output to last longer, or an edge detector if you need exactly one trigger.
Which side of an observer outputs the signal?
The observer outputs its pulse from the back — the face with the small dot — opposite the larger watching face. It detects changes only in the single block directly in front of the watching face and fires a 1-redstone-tick pulse.