Here's the prototype of a working safe-type combination lock. The three rotors turn independently moved by the spindle at the front of the model, the mechanism is difficult to explain but easy to demonstrate so you'll have to wait for the forth-coming video for full details. It just needs a dial on the front and it'll be "20 right, 112 left, 65 right, open!".
Once the three rotors are lined up the safe is unlocked and can be opened. Next step, fit the mechanism into a box with lockable compartment. My initial plan is to make a box with a small drawer, perhaps large enough to hold a ring or locket.
You can see the cat (Ruby) looking on through the window in the thumbnail picture. Meow!