It's been a while since I have posted something fun for the original NXT, as I have been distracted by NXT 2.0 recently... So here is something fun. This Combination Lock Box keeps the blue and red balls locked inside until you enter the correct combination using the dial wheel and Enter button, then it will unlock and open automatically. The first time you run the program, it will ask you to set your combination of three numbers, then it will remember this combination even when the NXT is off and only open the box when the correct combination is entered.
The building instructions and program are for the original NXT, and it is not buildable as designed here with NXT 2.0, but maybe some NXT 2.0 users will give a try at modifying it. The program should work on NXT 2.0 (like all NXT 1.X programs).
Here is a video of the box in action: