How do I make a Block Update Detector?

I am running the latest version of MCPE, so I don't have access to pistons, redstone repeaters, or redstone comparators. Is it possible to make a BUD switch?

Solution 1:

Yes, it is most definitely possible. To do this you must make something that the game won't allow you to do by simply placing blocks. There are 2 ways I know of doing this.
1.Sugarcane
An example of something the game won't allow you to do is planting sugar cane without water. You still can, however, plant sugarcane then get rid of the water, by either getting rid of the source or placing a block next to the sand or dirt that it is growing on. This doesn't touch the sugarcane blocks at all, and thus allows for them to continue existing as there was no block update adjacent to them. Once the water is gone, simply placing a block next to them will cause a block update and destroy them.

2.Water*
Water will attempt to flow, without spreading, into any hole within 5 blocks of its source. Ergo, you can make a flat surface with a 5 block radius around the water and only one hole. You can then destroy the surrounding floor blocks, making another hole within 5 blocks. This doesn't touch the water stream at all, so no block update. When you touch the stream at all after that, it should sense the new hole near it, and flow into it, spreading.

You can't really make these do anything interesting. You can, however, use a system of sand, torches, and water to make some interesting contraptions. Ill let you figure that out on your own :)

*There are more ways to do this with water, but that was the simplest.