View source for Observer

{{Block
|image=Observer.png
|image2=Observer (back).gif
|invimage=Observer
|transparent=Partial
|light=Yes
|tool=wooden pickaxe
|renewable=Yes
|stackable=Yes (64)
|flammable=No
|lavasusceptible=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.
{{breaking row|Observer|Pickaxe|Wood|horizontal=1}}

=== Crafting ===

{{Crafting
  |A1=Cobblestone
  |B1=Cobblestone
  |C1=Cobblestone
  |A2=Redstone Dust
  |B2=Redstone Dust
  |C2=Nether Quartz
  |A3=Cobblestone
  |B3=Cobblestone
  |C3=Cobblestone
  |Output=Observer
  |type=Redstone
}}

== 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 [[Mechanics/Redstone/Pulse circuit|pulse]].

=== Behavior ===

{{IN|java}}, 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}}, 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 [[Pulse circuit|redstone pulse]] of [[Redstone circuit#Power|strong power]] at level 15 for 2 [[game tick]]s (1 [[redstone tick]]). The pulse can power [[redstone dust]], a [[redstone comparator]], a [[redstone repeater]], or any [[Redstone components#Mechanism components|mechanism component]] located at its opposite end.

{{IN|java}}, 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 {{bug|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 {{bug|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 [[Tutorials/Block update detector|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 ===
{{testingame|cactus aging? bamboo aging or growing?}}
{| class="wikitable"
! 
! colspan="2" | Detected in
|-
! Kind of block update
! {{el|be}}
! {{el|je}}
|-
| {{BlockSprite|fire}} Changes to the block states of [[fire]] that signifies flammable surfaces surrounding fire
| {{tc|No}}
| {{tc|Yes}}
|-
| {{BlockSprite|chest}} {{BlockSprite|trapped-chest}} {{BlockSprite|ender-chest}} Opening and closing [[chest]]s and [[ender chest]]s
| {{tc|No}}
| {{tc|No}}
|-
| {{BlockSprite|shulker-box}} Opening and closing [[shulker box]]es
| {{tc|No}}
| {{tc|Yes}}
|-
| {{BlockSprite|barrel}} Opening and closing [[barrel]]s
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|chest}} Changes to [[inventory]] of any blocks that [[Redstone Comparator|comparator]]s measure as containers
| {{tc|No}}
| {{tc|No}}
|-
| {{BlockSprite|beacon}} Activating / deactivating a [[beacon]]
| {{tc|Yes}}
| {{tc|No}}
|-
| {{BlockSprite|command block}} Success of a [[command block]]
| {{tc|No}}
| {{tc|No}}
|-
| {{BlockSprite|hopper}} Activation / deactivation of a [[hopper]] (Turning the hopper on/off)
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|farmland}} Dry [[farmland]] changing among its six dry-looking hydration stages
| {{tc|No}}
| {{tc|Yes}}
|-
| {{BlockSprite|farmland wet}} [[Farmland]] going between dry and humid
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|dropper}} {{BlockSprite|dispenser}} Activation / deactivation of a [[dropper]] or [[dispenser]]
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|redstone ore}} Activation / deactivation of [[redstone ore]]
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|grass-block}} Spread of grass to [[dirt]], or decay of grass into dirt
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|saplings}} {{BlockSprite|sugar cane}} {{BlockSprite|fire}} Aging of [[sapling]]s, [[sugar cane]] or [[fire]]
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|brewing-stand}} Moving [[potion]]s to / from a [[brewing stand]]
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|dragon-head}} Activation / deactivation of a [[dragon head]]
| {{tc|Yes}}
| {{tc|No}}
|-
| {{ItemSprite|item-frame}} Placing / removing an [[item frame]], adding / rotating / removing an item in an item frame
| {{tc|Yes}}
| {{tc|No}}
|-
| {{BlockSprite|end-gateway}} Teleporting something by the [[end gateway]]
| {{tc|Yes}}
| {{tc|No}}
|-
| {{BlockSprite|flower-pot}} Adding / removing contents from a [[flower pot]]
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|redstone-repeater}} Locking / unlocking and changing delay of a [[redstone repeater]]
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|cobblestone wall}} {{BlockSprite|fences}} {{BlockSprite|iron-bars}} {{BlockSprite|blue-stained-glass}} {{BlockSprite|stairs}} {{BlockSprite|redstone-dust}} {{BlockSprite|tripwire}} {{BlockSprite|vines}} {{BlockSprite|melon-stem}} Changes in the shape of [[Cobblestone Wall|wall]]s, [[fence]]s, [[iron bars]], [[glass pane]]s, [[stairs]], [[String|tripwire]], [[redstone]], [[vines]], [[melon stem]]<ref name="note">Melon or pumpkin stems that become attached to the melon or pumpkin are detected in Java Edition, and Bedrock Edition.<!--if that's the case shouldn't they be split so it doesn't say yes?--></ref> or [[pumpkin stem]]<ref name="note"/>
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|grass-block}} {{BlockSprite|mycelium}} {{BlockSprite|podzol}} A [[Grass Block|grass]], [[mycelium]], or [[podzol]] block becoming snowy or not snowy
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|note-block}} Playing a [[note block]]
| {{tc|No}}
| {{tc|Yes}}
|-
| {{BlockSprite|sugar-cane}} Forced growth of [[sugar cane]] by [[bone meal]]
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|campfire}} {{BlockSprite|soul-campfire}} Cooking food or food popping out
| {{tc|Yes}}
| {{tc|No}}
|-
| {{BlockSprite|oak-door}} {{BlockSprite|spruce-door}} {{BlockSprite|birch-door}} {{BlockSprite|jungle-door}} {{BlockSprite|acacia-door}} {{BlockSprite|dark-oak-door}} {{BlockSprite|iron-door}} [[Door]] is opened or closed
| {{tc|Yes}}
| {{tc|Yes}}
|-
| {{BlockSprite|tripwire}} [[Tripwire]] is intersected, even if not attached to a hook
| {{tc|Yes}}<ref name="note 2">Includes firework rockets, falling block entities, fishing hooks, entities (ie. fireballs, lama spit, evoker fangs etc.) and all throwable projectiles other than splash/lingering potions and enderpearls.</ref>
| {{tc|Yes}}
|-
| All other [[block]] / [[block state]] changes
| {{tc|Yes}}
| {{tc|Yes}}
|-
| Water level changes
| {{tc|Yes}}
| {{tc|Yes}}
|}

=== Note Blocks ===
The observer can be placed under [[note block]]s to produce a "bass drum" sound.

== Sounds ==
{{Sound table/Block/Stone}}

== Data values ==
=== ID ===
{{edition|java}}:
{{ID table
|showforms=y
|generatetranslationkeys=java
|displayname=Observer
|spritetype=block
|nameid=observer
|foot=1}}

{{edition|bedrock}}:
{{ID table
|shownumericids=y
|showforms=y
|generatetranslationkeys=bedrock
|displayname=Observer
|spritetype=block
|nameid=observer
|id=251
|foot=1}}

=== Metadata ===
{{see also|Data values}} 
{{IN|be}}, observers use the following data values:
{{/DV}}

=== Block states ===
{{see also|Block states}}
{{/BS}}

== History ==
{{History|java}}
{{History||November 24, 2012|link= https://youtube.com/watch?v=YG9RNyRhIow?t=5m42s|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.}}
{{History||1.11|snap=16w39a|[[File:Observer JE1.png|32px]] 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 [[Tutorials/Block update detector|block update detector]].
|Observers emit pulses that lasted 1 [[Tick#Game tick|game tick]] (0.5 [[Tick#Redstone tick|redstone ticks]]) and have a signal strength of 1.
|Observers can power [[block]]s (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]].}}
{{History|||snap=16w41a|Observers now emit 4 [[Tick#Game tick|game tick]] (2 [[Tick#Redstone tick|redstone ticks]]) pulses.<ref>{{bug|MC-107410}}</ref>
|The signal strength of observers has now been changed to 15.<ref>{{bug|MC-107783}}</ref><ref>{{bug|MCPE-17439}}</ref>
|Observers *appear* to no longer strongly power [[block]]s, 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.<ref>{{bug|MC-108696}}</ref>
|Observers are now placed with the output facing the player.<ref>{{bug|MC-107934}}</ref><ref>{{bug|MCPE-17321}}</ref>
|A bug where observers would redirect [[redstone dust]] from all 4 directions has now been fixed.<ref>{{bug|MC-107795}}</ref> (They are supposed to redirect dust only from their output side.)}}
{{History|||snap=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.<ref>{{bug|MC-107730}}</ref> In the process, they have broken [[redstone]] mechanics a bit, so that the block update bug from the previous snapshot now affects [[redstone repeater]]s and [[redstone comparator]]s, too.<ref>{{bug|MC-108897}}</ref>}}
{{History|||snap=16w43a|[[File:Observer JE2.png|32px]] The texture{{verify|this was much more likely a model change}} 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 [[Java Edition 16w42a|16w42a]], with the exception of the change named below.
|Observers now output strong power like in 16w39a, except that they, as well as [[redstone repeater]]s and [[redstone comparator]]s, no longer provide block updates to transparent [[block]]s or [[air]].}}
{{History|||snap=16w44a|The observer [[block]] update changes relating to [[redstone]] from [[Java Edition 16w42a|16w42a]] and [[Java Edition 16w43a|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.<ref>{{bug|MC-107760}}</ref>
|Observers have now been changed to emit a 2 [[Tick#Game tick|game tick]] (1 [[Tick#Redstone tick|redstone tick]]) pulse when activated.<ref>{{bug|MC-108697}}</ref>
|Observers no longer output power instantly.<ref>{{bug|MC-107623}}</ref>}}
{{History|||snap=pre1|[[File:Observer JE3.png|32px]] 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.}}
{{History||1.13|snap=17w47a|Prior to [[1.13/Flattening|''The Flattening'']], this [[block]]'s numeral ID was 218.
|Due to [[1.13/Flattening|''The Flattening'']], observers can now detect all block state changes, e.g. the changes in the shape of [[fence]]s and [[redstone dust]].}}
{{History|||snap=pre4|Observers no longer produce a pulse when placed by hand.}}
{{History||1.14|snap=18w43a|[[File:Observer JE4 BE3.png|32px]] [[File:Observer (back) JE1 BE1.gif|32px]] 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.<ref>{{bug|MC-199231}}</ref>}}
{{History||1.16|snap=20w10a|Observers can now support [[ladder]]s and [[tripwire hook]]s.<ref>{{bug|MC-146824}}</ref>}}
{{History|||snap=20w14a|Observers now correctly detect when the status of the fence changes.}}
{{History|||snap=Pre-release 3|[[File:Observer (back) JE2.gif|32px]] The back texture of activated observers has been changed.}}
{{History|Upcoming java}}
{{History||1.17|snap=21w13a|Observers now correctly detect when a [[grass block]] changes to [[dirt]] if a tree grows on top.}}

{{History|pocket alpha}}
{{History||v0.15.0|snap=May 2, 2016|slink=none|[[Jeb]] tweeted that [[Daniel Wustenhoff]] is a working on a [[Tutorials/Block update detector|BUD]] block.<ref>{{tweet|jeb|727043609552367616|Hype train! @darngeek is working on a device that acts as a proper BUD block in MC:PE (PC eventually), currently called "Observer"|May 2, 2016}}</ref>
|[[File:Observer (front texture) pBE20160502.png|32px]] [[Tommaso Checchi]] tweeted his "rejected graphics" for the observer [[block]].<ref name="ReferenceA">{{tweet|tomcc|727044087522713600|Here's my rejected graphics for the Observer, because @darngeek has no artistic sensibility|May 2, 2016}}</ref>}}
{{History|||snap=build 1|[[File:Observer BE1.png|32px]] Added observer blocks.}}
{{History||v0.15.3|Observers are now placed like a [[piston]] and not a [[log]].}}
{{History|bedrock}}
{{History||1.2.0|snap=beta 1.2.0.2|[[File:Observer BE2.png|32px]] 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.}}
{{History||1.10.0|snap=beta 1.10.0.3|[[File:Observer JE4 BE3.png|32px]] The texture of observers has now been changed.}}
{{History||1.16.0|snap=beta 1.15.0.53|Observers no longer emit a pulse when they are first placed.}}
{{History||1.16.100|snap=beta 1.16.100.55|Observers no longer get stuck in an active state when moved by [[pistons]].}}

{{History|console}}
{{History||xbox=TU54|xbone=CU44|ps=1.52|wiiu=Patch 24|switch=1.0.4|[[File:Observer JE3.png|32px]] Added observers.}}
{{History||xbox=none|xbone=none|ps=1.90|wiiu=none|switch=none|[[File:Observer JE4 BE3.png|32px]] The texture of observers has now been changed.}}

{{History|3ds}}
{{History||0.1.0|[[File:Observer BE1.png|32px]] Added observers.}}
{{History|foot}}

== Issues ==

{{issue list}}

== 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 [[Jens Bergensten|Jeb]] kept confusing the front with the back. He said it was inspired by the "rejected texture" created by Tommaso Checchi.<ref name="ReferenceA">{{tweet|tomcc|727044087522713600|Here's my rejected graphics for the Observer, because @darngeek has no artistic sensibility|May 2, 2016}}</ref><ref>{{tweet|jeb_|795625080067866624|I kept confusing myself which side was front and back, so here's something inspired by the works of @_tomcc http://i.imgur.com/IK2d8m2.png}}</ref>

== Gallery ==

<gallery>
File:Frowny Observers.png|The first image released of the new observer texture for the Java Edition
</gallery>

== See also ==
* [[Tutorials/Block update detector]]
* [[Redstone Comparator]]

== References ==
{{reflist}}

{{redstone}}
{{blocks}}

[[Category:Mechanisms]]
[[Category:Manufactured blocks]]

[[de:Beobachter]]
[[fr:Observateur]]
[[ja:オブザーバー]]
[[ko:관측기]]
[[nl:Observeerder]]
[[pl:Detektor]]
[[pt:Observador]]
[[ru:Наблюдатель]]
[[zh:侦测器]]