False Stair Tread
It takes some effort, but if you can, free a tread from your stairs. Then attach a piano hinge to the back. It'll be almost invisible and you'll have a good place to stash valuables.
Time Well Spent
Store a few small items in a wall or mantel clock, as long as the clock itself isn’t worth stealing! Tape them to the back or put them in any open cavities. Steer clear of these hiding places, because that’s where burglars always look first!