This is a very small, very efficient, very cool block update detector, or BUD. While most conventional BUDs use pistons, this one uses no pistons at all. The only sound you hear is the burning out of the Redstone torches. The only thing to remember is to use my pulse inverter with the output repeater at 3 ticks in order to reduce it down to one. The "update zone" is anywhere adjacent to the front torch.

Additional Notes

Pulse Inverter Link: http://www.planetminecraft.com/project/pulse-inverter/