The locked door is an iron door with an item frame on its side. To open the door, you have to turn the item frame item to the correct position. To build it, first build the door against the wall. Keep a good distance between the door and the item frame. Put a redstone comparitor behind the item frame. Put 15 redstone wires behind the comparitor. Put an item in the item frame and turn it to the correct position (the position you choose). Now, change the second block of redstone dust with strength 0 to a block and put a redstone torch on the other side of the block. Put a repeator next to the redstone dust with strength 1. Put a block next to the repeator and a redstone torch on top of the block. Connect the other redstone torch to a block and put a redstone torch on top. Now, connect the redstone torches that are on top of blocks. Now, put a redstone torch on the side of a block that has the connecting redstone dust. Connect the redstone torch to a block. Put a redstone torch on the other side of the block. Put a redstone torch 2 blocks under the door on the side of another block. Now, connect the block to the other redstone torch! To lock the door now, turn the item in the item frame to a different position.