This safe seems like it would be particularly secure if you recessed it into the wall and then mounted it high up so that you needed a ladder to get to it.
From the product description:
At a glance, it looks like any other regular wall clock. But you know the secret! It swings open to store your valuables and small mementos on three shelves. Clock runs on 1 AA battery, not included. Has three predrilled mounting holes, hardware not included. Outside dimensions: 10"dia. by 3"deep. Inside: 8.5" dia. by 1.75" deep.
Here the link to the Wall Clock With Hidden Safe