I've seen a few combination safes on youtube, but they all used an at least 5 times bigger mechanism than this one. So if you build this safe you have less chance to run out of lego bricks before you're finished.
IMPORTANT: Before you decide to build this, look at the second picture below! Those are the fancy pieces needed. The first, the nine curved bricks, are absolutely required, but not necessarily in red. The two springs, are not extremely important; without it, the door doesn't 'jump' open as you can see in the video below. All other pieces I used, are common lego pieces which belong in an average lego collection, or are well replaceable by a surrogate.
So if you decide to build it, proceed to the next step!