Hidden Keypad

From Glitches

From the game Maniac Mansion for the NES.

In the long second floor hallway with the two doors that lead to the lab and the arcade room, go near the very left end and search around the wall near the base of the Steel Security Door. You should eventually find an invisible Keypad. If you use it enough times in a row, the house will explode. But even if you just use it once, the countdown alarm will start and eventually the house will explode anyway. The moral of the story is...don't use it. But the question remains...why is it even there? It's a remnant of something that was only in the PC version. Many early DOS PC games had security features to discourage people from making illegal pirate copies of them. In the PC version of Maniac Mansion, the Steel Security Door had a keypad on it and you had to enter a code to get past it. The codes could only be found in a code booklet that came with the game. If you entered the wrong code too many times, the house would explode and end your game. Now, why the Keypad was not just taken out of the NES version altogether still remains a mystery.

Taken with permission from Flying Omelette.