Observer

Observer

Renewable	Yes
Stackable	Yes (64)
Tool
Blast resistance	3.5
Hardness	3.5
Luminant	Yes
Transparent	Partial
Flammable	No
Catches fire from lava	No

An observer is a block that emits a redstone signal when the block or fluid it faces experiences a change.

Obtaining

Breaking

An observer requires a pickaxe to be mined. When mined without a pickaxe, it drops nothing.

Block	Observer
Hardness	3.5
Tool
Breaking time
Default	17.5
Wooden	2.65
Stone	1.35
Iron	0.9
Diamond	0.7
Netherite	0.6
Golden	0.45

Crafting

Ingredients	Crafting recipe
Cobblestone + Redstone Dust + Nether Quartz

Usage

An observer is placed similarly to a piston. It observes the block that it is placed against. The texture of the detecting side is that of an observing face. As observers can detect the state of other observers, placing two adjacent observers, each watching the other, can make a fast and compact redstone clock. They send out a pulse.

Behavior

In Java Edition, an observer detects changes in its target's block states, or the breaking or placing of a block (i.e. changes in its block state, but not its block entity data). This means that changes like the age of crops can be detected because they are part of the block states.

In Bedrock Edition, an observer acts as a block update detector and detects anything that causes a block update.

The causes and propagation of block updates are different between Java Edition and Bedrock Edition. As a result, each can detect some kinds of changes that the other cannot. See the table below for a comparison.

When it detects something, the observer emits a redstone pulse of strong power at level 15 for 2 game ticks (1 redstone tick). The pulse can power redstone dust, a redstone comparator, a redstone repeater, or any mechanism component located at its opposite end.

In Java Edition, the pulse is emitted with a delay of 1 redstone tick. In Bedrock Edition, it is supposed to be delayed by 1 tick as well but is actually delayed 2 redstone ticks due to MCPE-15793, a bug causing redstone delays to be incorrect when components are activated by world changes (which, in the case of the observer in Bedrock Edition, is the only way it can be activated), as opposed to pure redstone components ticking. Its timing can also be incorrect due to MCPE-73342.

It also counts as a block update when the observer itself is moved by a piston. When this happens, an observer emits a pulse after being pushed or pulled, but not beforehand.

Though they block light, observers behave as transparent blocks in one sense: they cannot be powered by an external power source, nor power themselves with their own output.

Because observers in Java Edition detect changes in the block state, and not block updates, they can detect a wider range of phenomena than a block update detector (BUD) circuit in Java Edition can detect (as some block state changes don't cause block updates). Observers in Bedrock Edition do detect block updates but not block state changes, and so they detect the exact same things that any other BUD would detect in that edition.

Limitations

^{[needs in-game testing]}

	Detected in
Kind of block update	Bedrock Edition	Java Edition
Changes to the block states of fire that signifies flammable surfaces surrounding fire	No	Yes
Opening and closing chests and ender chests	No	No
Opening and closing shulker boxes	No	Yes
Opening and closing barrels	Yes	Yes
Changes to inventory of any blocks that comparators measure as containers	No	No
Activating / deactivating a beacon	Yes	No
Success of a command block	No	No
Activation / deactivation of a hopper (Turning the hopper on/off)	Yes	Yes
Dry farmland changing among its six dry-looking hydration stages	No	Yes
Farmland going between dry and humid	Yes	Yes
Activation / deactivation of a dropper or dispenser	Yes	Yes
Activation / deactivation of redstone ore	Yes	Yes
Spread of grass to dirt, or decay of grass into dirt	Yes	Yes
Aging of saplings, sugar cane or fire	Yes	Yes
Moving potions to / from a brewing stand	Yes	Yes
Activation / deactivation of a dragon head	Yes	No
Placing / removing an item frame, adding / rotating / removing an item in an item frame	Yes	No
Teleporting something by the end gateway	Yes	No
Adding / removing contents from a flower pot	Yes	Yes
Locking / unlocking and changing delay of a redstone repeater	Yes	Yes
Changes in the shape of walls, fences, iron bars, glass panes, stairs, tripwire, redstone, vines, melon stem or pumpkin stem	Yes	Yes
A grass, mycelium, or podzol block becoming snowy or not snowy	Yes	Yes
Playing a note block	No	Yes
Forced growth of sugar cane by bone meal	Yes	Yes
Cooking food or food popping out	Yes	No
Door is opened or closed	Yes	Yes
Tripwire is intersected, even if not attached to a hook	Yes	Yes
All other block / block state changes	Yes	Yes
Water level changes	Yes	Yes

Note Blocks

The observer can be placed under note blocks to produce a "bass drum" sound.

Sounds

Java Edition:

Sound	Subtitles	Source	Description	Namespaced ID	Translation key	Volume	Pitch	Attenuation distance
	Block broken	Blocks	Once the block has broken	block.stone.break	subtitles.block.generic.break	1.0	0.8	16
	None	Blocks	Falling on the block with fall damage	block.stone.fall	None	0.5	0.75	16
	Block breaking	Blocks	While the block is in the process of being broken	block.stone.hit	subtitles.block.generic.hit	0.25	0.5	16
	Block placed	Blocks	When the block is placed	block.stone.place	subtitles.block.generic.place	1.0	0.8	16
	Footsteps	Blocks	Walking on the block	block.stone.step	subtitles.block.generic.footsteps	0.15	1.0	16

Bedrock Edition:

Sound	Source	Description	Namespaced ID	Volume	Pitch
	Blocks	Once the block has broken	dig.stone	1.0	0.8
	Blocks	Falling on the block with fall damage	fall.stone	0.4	1.0
	Blocks	While the block is in the process of being broken	hit.stone	0.37	0.5
?	Blocks	Jumping from the block	jump.stone	0.12	1.0
?	Blocks	Falling on the block without fall damage	land.stone	0.22	1.0
	Blocks	Walking on the block	step.stone	0.3	1.0
	Blocks	When the block is placed	use.stone	1.0	0.8

Data values

ID

Java Edition:

Name	Namespaced ID	Form	Translation key
Observer	observer	Block & Item	block.minecraft.observer

Bedrock Edition:

Name	Namespaced ID	Numeric ID	Form	Translation key
Observer	observer	251	Block & Item	tile.observer.name

Metadata

See also: Data values

In Bedrock Edition, observers use the following data values:

Bits	Values
0x1 0x2 0x4	Three bits storing a value from 0 to 5: 0: Observer facing down 1: Observer facing up 2: Observer facing north 3: Observer facing south 4: Observer facing west 5: Observer facing east
0x8	If set, the observer is powered.

Block states

See also: Block states

Java Edition:

Name	Default value	Allowed values	Description
facing	south	down east north south up west	The direction the observer is observing. The same direction the player faces when placing the block.
powered	false	false true	True while the observer is observing a change and emitting a pulse.

Bedrock Edition:

Name	Default value	Allowed values	Description
facing_direction	0	0 1 2 3 4 5	The direction the observer is observing. The same direction the player faces when placing the block.
powered_bit	0	0 1	True while the observer is observing a change and emitting a pulse.

History

Java Edition
November 24, 2012					When announcing the upcoming 1.5 Redstone Update, Jeb mentions that changes to redstone logic may break existing BUD functionality, and therefore that block update detection may need to be implemented into the game in a more permanent, intentional form, rather than as a behavioral quirk.
1.11		16w39a			Added observers.
					Note: the "arrow" texture on the top/bottom of observers is pointing the wrong direction (toward the input, rather than the output).
					Observers act as a block update detector.
					Observers emit pulses that lasted 1 game tick (0.5 redstone ticks) and have a signal strength of 1.
					Observers can power blocks (like a redstone repeater).
					Observers have no delay between detecting a block update and emitting a pulse, meaning that observers are essentially instant.
					Observers are placed with the observing, or input, side facing the player.
		16w41a			Observers now emit 4 game tick (2 redstone ticks) pulses.
					The signal strength of observers has now been changed to 15.
					Observers *appear* to no longer strongly power blocks, and now emit only activation power, like a block of redstone (and this may be the intended behavior for this snapshot). However, in reality, they still strongly power blocks, but the blocks adjacent to those blocks aren't given block updates, causing buggy behavior.
					Observers are now placed with the output facing the player.
					A bug where observers would redirect redstone dust from all 4 directions has now been fixed. (They are supposed to redirect dust only from their output side.)
		16w42a			The developers have attempted to make observers no longer detect block updates happening to air blocks, in order to make observer behavior more predictable. In the process, they have broken redstone mechanics a bit, so that the block update bug from the previous snapshot now affects redstone repeaters and redstone comparators, too.
		16w43a			The texture[verify] of observers has now been changed. The rotation of the "arrow" texture has now been fixed so it points in the correct direction.
					General redstone mechanics for observers now work as they did before 16w42a, with the exception of the change named below.
					Observers now output strong power like in 16w39a, except that they, as well as redstone repeaters and redstone comparators, no longer provide block updates to transparent blocks or air.
		16w44a			The observer block update changes relating to redstone from 16w42a and 16w43a have now been fully reverted.
					The behavior of observers has now been overhauled/redefined. Observers have now been changed from a block update detector to a block state change detector.
					Observers have now been changed to detect when the block it was observing changed, its basic block state changed, or the block was placed/destroyed. (Note that it does not detect changes in the extended block state, e.g. changes that are not saved when the world is unloaded, such as the shape of a fence, or whether or not a repeater is locked.) This change has now made observer behavior much more predictable, as unexpected/invisible block updates would no longer trigger observers.
					Observers have now been changed to emit a 2 game tick (1 redstone tick) pulse when activated.
					Observers no longer output power instantly.
		pre1			The front (detecting side) texture of observers has now been changed to be an 'observing face'. The "arrow" texture on the top/bottom of the observer has also been modified.
					The redstone output side of observers now blinks red when it outputs power.
1.13		17w47a			Prior to The Flattening, this block's numeral ID was 218.
					Due to The Flattening, observers can now detect all block state changes, e.g. the changes in the shape of fences and redstone dust.
		pre4			Observers no longer produce a pulse when placed by hand.
1.14		18w43a			The texture of observers has now been changed. The top face is still largely based on the old, pre-Texture Update furnace/dispenser/dropper "smooth cobblestone" texture, rather than its updated Texture Update version, which has since been confirmed to be fully intentional.
1.16		20w10a			Observers can now support ladders and tripwire hooks.
		20w14a			Observers now correctly detect when the status of the fence changes.
		Pre-release 3			The back texture of activated observers has been changed.
1.17		21w13a			Observers now correctly detect when a grass block changes to dirt if a tree grows on top.
Pocket Edition Alpha
v0.15.0		May 2, 2016			Jeb tweeted that Daniel Wustenhoff is a working on a BUD block.
					Tommaso Checchi tweeted his "rejected graphics" for the observer block.
		build 1			Added observer blocks.
v0.15.3					Observers are now placed like a piston and not a log.
Bedrock Edition
1.2.0		beta 1.2.0.2			The texture of observers has now been changed.
					Observer blocks can now detect many more block changes.
					The strength of the redstone pulse outputted by observer blocks has now been increased.
					Observers no longer pulse twice when observing a retracting piston.
					Opening and closing the command block screen no longer activates an observer block.
1.10.0		beta 1.10.0.3			The texture of observers has now been changed.
1.16.0		beta 1.15.0.53			Observers no longer emit a pulse when they are first placed.
1.16.100		beta 1.16.100.55			Observers no longer get stuck in an active state when moved by pistons.
Legacy Console Edition
TU54	CU44	1.52	Patch 24	1.0.4	Added observers.
		1.90			The texture of observers has now been changed.
New Nintendo 3DS Edition
0.1.0					Added observers.

Issues

Issues relating to "Observer" are maintained on the bug tracker. Report issues there.

Trivia

• When moved by a piston, an observer sends a 2-game tick (1 redstone tick) pulse after being moved, which makes it useful for slime block flying machines.
• The current Observer texture was created because Jeb kept confusing the front with the back. He said it was inspired by the "rejected texture" created by Tommaso Checchi.

Gallery

• 

  The first image released of the new observer texture for the Java Edition

See also

• Tutorials/Block update detector
• Redstone Comparator

References

Redstone

View at: Template:Redstone/content [edit]