The Observer block is a BUD (Block Update Detector) block that will send a short Redstone pulse if the block it is facing gets updated (mined, placed, etc.). They are placed like Pistons. The Observer will detect block updates on the face of the larger red square. When placed, this will be the face furthest to the Player. Hence, the Player should look towards the Block where the Block updates will occur when placing an Observer. The Observer texture that Tommaso Checchi created.