Tutorials/Block update detector

A Block Update Detector, also popularly known as a BUD switch (term coined by Etho), detects block updates using vanila game mechanics.

The method was discovered by Cored.

Cored's publishing of the discovery

It was later re-introduced by Etho, gained popularity, and many other variations of the BUD have been made

What it detects
A block update detector detects block updates (changes of block ID, data value, or its powered status) at specific coordinates, including:


 * Placement of blocks
 * Destruction of blocks
 * Flowing water or lava
 * Gravel or sand landing in a watched space
 * Growth of wheat, trees, mushrooms and sugar cane
 * Leaf growth and decay
 * Growth of grass
 * Dirt becoming tilled soil, soil becoming moist, soil reverting to dirt
 * This can be done without a BUD, as farmland does not transmit current, while dirt does.
 * Flashing redstone ore
 * Setting the delay on a repeater
 * Redstone power updates
 * This includes not only wires/torches/repeaters changing state, but also blocks updating due to placement of nearby wire, which effectively extends the range of piston-based BUDs to 2 blocks.
 * Player laying down on a bed (an occupied bed block is a different block)
 * Furnace stopping and starting smelting (as a lit furnace is a different block)