Minecraft wiki entry for Combination_locks, associated text: For a lock that can have a combination of any size, using all the buttons, and still have a wrong entry reset the system, you need a different way for it to reset. To construct this, hook up a panel of buttons (any number, but four or more is preferred) to a parallel series of adjacent repeaters. Invert as necessary so that all the repeaters are powered and are unpowered by the press of the corresponding button. These repeaters power a row of blocks. On top of the blocks, place a torch corresponding to the incorrect buttons for the fist number in the PIN. For the correct button/number, place dust under the powered block which leads to a RS NOR Latch. Place a row of blocks above the torches for the incorrect buttons, with redstone dust on top. Then connect this dust to the reset of the first RS NOR Latch. Only the correct button will set the RS NOR Latch and all others will reset it. Connect the output of the RS NOR LATCH to half of an AND gate. After the first row of blocks with the reset torches, place another row of repeaters and another row of blocks. Again place torches for the incorrect buttons and dust under the correct button's line. Power will be fed from the buttons through the rows of repeaters and blocks for as many rows as there are digits in the PIN number. Connect the dust from the correct button to the other half of the AND gate coming from the first RS NOR Latch. Only if the two conditions are met, that the first button was pushed correctly, setting the first RS NOR Latch, and the second button is pushed correctly will the AND gate send a signal to set the second RS NOR Latch. Again, connect a reset line from the incorrect button's torches to the reset of the second RS NOR Latch. Delay the reset signals by one full repeater to give time for the next RS NOR Latch to be set before the reset happens. Continue building the array in the same manner until you reach the desired number of digits. In operation, when a button is hit, each RS NOR Latch checks (through the AND gate) to see if the previous RS NOR Latch is set, and the correct button for this RS NOR Latch has been pushed. Only when the correct buttons are pressed in order, will the signal progress through the conditional RS NOR Latches to the end. Connect the output of the last RS NOR Latch to a door and attach a line to a pressure plate inside the door to reset the last RS NOR Latch.