(I only tested this horizontally) A piston (any will do), a slime block in front of the piston, a block on either side of the piston with redstone on top, and then place an observer block facing opposite from where the iron block is, next to the slime block; the redstone will lock up in a power state of 1 and it will BUD.(i mean it COULD be useful in some cases, but i wouldn't know when it could)
https://youtu.be/wcz4Vbebq-s