Hi gang!A few days ago our own Kyzoy suggested a new flag to stop pressure plates from responding. Because I once made a redstone circuit quite a few months ago which does just that I talked to Kyzoy today, showed him my solution and he showed me the actual problem he was having. It immediately looked quite intriguing to me because I immediately spotted something weird:The problem at handIf you step on the pressure plate nothing happens, but once you move away from it the wooden trapdoor will close. At first sight this might seem logical: the trapdoor is a redstone power source after all so it probably powered the trapdoor which then got closed when the power went down.But here's where things become interesting: that can't be the case. In the above picture the only block which would get directly powered by the pressure plate is the block below it. This block gets a so called "strong charge"; this means that blocks in its direct surrounding can "pick up" this redstone signal (I won't explain here, if you want to know more you'll have to wait for my upcoming redstone tutorial). But the block to which the trapdoor is attached is way up in the air. There is no way that this charge could ever reach it!Here is a more obvious example:All the sandstone you see here are slabs. And slabs have a unique ability: they cannot provide a redstone charge to other blocks in the vicinity. I demonstrated as much with the redstone dust you see behind it. Would this have been a normal sandstone block then that redstone dust would get charged, and lit up the redstone lamp. Yet that doesn't happen.But even if it did: you'll also notice that the block with the trapdoor attached to it is waay up in the air. There is no way that the redstone signal can reach it.And it gets even better If I place some redstone dust next to the pressure plate then the trapdoor also automatically closes:Block Update DetectorNow... I'm decently experienced with redstone and I can conclude that this has nothing to do with redstone at all. So what is it?My theory: this is a crude BUD switch, aka Block Update Detector. A BUD switch remains idle until something in its vicinity changes, usually the placement of a block. When that happens the BUD switch will then "do" something.So far my theory. As said: I'm experienced with redstone but not that much with BUD switches.As such my post here: what do you think dear reader?If you'd like to see for yourself then you can visit 3544 (on SMP2). Behind the main stairs is a trapdoor (which will be open for the rest of the day, no need to donate) and you can see for yourself.