I read about someone making an invisible lock/latch using a nail and a
magnet - have the nail sunk through a piece of small stock inside the
compartment which can pivot and the nail end can fall into a hole.
When you move a magnet up past the nail on the outside of the
compartment, the nail lifts out of the hole and releases the latch.
Did that make sense? Sorry - it sounds confusing, and it may be more
complex than you need, but it's really not a difficult concept and I
think it would be fun to try. (This idea came from a book by Kary
Mullis, inventer of the Polymerase Chain Reaction, if there are any
other woodworking molecular biologists out there...)