This redstone device is a combination lock, which is easy to modify, and does not require breaking any blocks to program, or any knowledge of the way it works. This version is 4-digits, with a 4-digit length password. It has very few components: the user interface, the RS-NOR latch array, and the programming interface.

Additional Notes

To program:
1: Go to the programming interface (the piston contraption on top) and flip levers for each number starting from back to front. You MUST power all levers in front of the position of the actual digit.
2: Press the button beside the programming interface.
3: Make sure you keep the correct levers powered after you press the button.
To use:
1: Enter the digits into the user interface.
2: If the light turns on, you got it correct.
3: Otherwise, press the button on the diamond block.