What Does An Observer ACTUALLY See?

A complete list of literally EVERYTHING that an observer can detect. Hopefully at least... Research was crazy...

Chapters:
00:00 Intro
00:28 What does an observer do?
01:51 The Common Denominator
02:20 Building Blocks
03:21 Colored Blocks
03:57 Natural Blocks
10:08 Functional Blocks
12:10 Redstone Blocks
15:31 Broad Categories
16:59 Special Cases
17:51 Outro

[yowza]

I genuinely enjoy the imagery of an observer getting so briefly excited it momentarily shits itself energy for a tick and immediately regains stoic composure

[Mr.Carrot]

At this point, a list of what the observers *can't* detect would be more useful

[WhoosferPlus]

"when it grows" my fav line of this video

[caspermadlener]

1. Redstone ore doesn't power when you place a block against it, only when you right or left click it. This is noticeable when you shift-click a block against it.
2. You forgot the dragon egg.
3. Pistons heads aren't oberved when trying to retract slime over pull limit.
4. When you clip the end of some plants, it is detected.

[xecron]

For those wondering what condition the observer checks, it typically reads the *blockstate* in front of it. A blockstate is a variable containing data on the block at that XYZ position which is used to change how certain blocks behave, how they look, and (you guessed it) to detect changes at a point. When the block in front of an observer is removed, placed, or updated through some behavior or player interaction. The data in the blockstate is changed, which is detected by the observer resulting in it sending a signal behind it.

Also, the data within the observer's blockstate is changed when it detects something, which is why you can chain observers.

[mooing_cowmilk]

One major thing observers can't detect is rapid changes, which breaks most age based farms, or fast tick block streams. Other items it can't detect is the creation of the nether portal block (lighting a nether portal), change text color of signs, left clicking a note box (in survival plays it but not detect).

[broski]

My two favourite are string when an entity enters or leaves it's hitbox, and note blocks when you change the instrument underneath.
I used the string one to make an automatic water dispenser for the riptide enchantment. When you stand in it, it dispenses water at your feet so you can riptide, and then when you leave, it triggers the dispenser again, getting rid of the water.
I've never really used the note block one, but it's a neat mechanic which can help you distinguish between blocks in some scenarios, like a block stream.
Edit: |-_-|

[Juni_Dingo]

Such a criminally underrated channel, you deserve so much more attention |-_-|

[FarTheGoober]

Genuinely couldn’t believe how small this channel was. Video quality is amazing and it’s clear you put a lot of time and effort into this video!! I’ll be glad to be along the ride do you getting famous because this deserves more recognition!

[Kokonutzlz]

9:17 it should also detect when the sponge evaporates :) It's not just a furnace recipe, it happens automatically in the Nether.

The string thing is really cool, as you don't need a more visible tripwire hook setup to activate it getting walked on. The hard part is now to hide the observer 🤔

[mimixte]

I already knew what the observer is used for but I must admit that some of these where new to me (like the scaffolding or the leaves), thank you for this amazing lesson professor |-_-|

[kirisummer]

I would categorize updates a bit differently, since lots of interactions could be described as "replacing an observed block", like when blocks are turned into moss or (cobble)stone from lava and water interactions, "changing amount" for turtle eggs, sea pickles or candles, or being more concise with grouping all "growable" blocks (crops, trees, bamboo, etc) into one category, but it's a good video nonetheless C:

[KidPrarchord]

Thank you for doing this! I remember thinking the scaffolding one was cool when I figured it out, so I'm glad to see that little trick being spread to a wider audience.

[lordmarum]

Very clear and fun to watch. Great videos!

[beefox__]

a common denominator for most of these are blocks and block states, anything that changes a block state (stair shape), or the block entirely (dirt turning to grass), there are some exceptions to this rule

[EquaTechnologies]

The observers can activate also when leaves are "charged" by wood. Nice video too!

[steelspyder]

You're gonna be huge someday!
Awesome Job dude... I love everything about this video

[Creepslime]

I have no plans of concocting complicated redstone contraptions myself, but the knowledge of the extent of what the |-_-| can do ought to be somewhat useful 👍

[wChris_]

Its actually pretty simple. |-_-| detect block state changes, i.e. if you open F3 the things at the lower right when looking at blocks. Block state changes also include blocks changing outright, like converting grass to dirt, because they are 2 distinct blocks.

[mrmurpleqwerty]

Nobody:
Almost every Natural Block: When it grows.


Coral: When it dries up and dies.