Ow, stop throwing 500A contactors at me, analogue folk! ;)

As you suggest, a transistor would work, though wiring the power directly to the Arduino probably would not. A relay is a bit overkill, but maybe he wanted the satisfying click of it kicking in?

If you want to prevent someone from easily just bypassing the code you could cover it all with epoxy – sure it wouldn’t prevent the most stubborn but it would stop it being easy.

Despite it not being very practical it’s a nice hack, and some of the best ones aren’t practical.

overall a wonderful start, i hope he moves it up to a larger storage of solid state drive and remolds the case and seals it with epoxy. this has a lot of potential

On a related note, this would be cool to use as some sort of door access system (if you could set up a timeout to prevent brute forcing). Another option would be to unplug the controller from the door (and carry it with you like a key). With the micro controller storing the last ten buttons even on a successful code entry, there’s a slight problem if someone ever gains read access to that array. But then again, I would go with a brute force attempt first knowing that you only have 8 buttons… we can infer that he’s pressing 10 buttons and then estimate that there are just over 1.073 billion options… given the UI, I would start the brute force at UUDDLRLRAB as a guess to try and shorten the number of combinations tried before success.

But who cares? This is up there with the external hard drive hidden in an old battery-less uninterrupted power supply. Nice work Joven.