I asked this before, but I didn't specify how I imagined it. So, you have an iron door, and a button besides it. You press the button with the keycard equal or higher than the level of the card reader, and it opens. If the keycard's level is lower than what the card reader (button) accepts, it closes the iron door instantly, and displays something like "You need level <number> to open this!" or something. I hope someone can help me. I appreciate all people helping.