Great idea for hiding guns in the house if you don't have a gun safe. Or even other items you want to keep safe! It took me a little while to understand this. The shelf unit slides behind a mirror. I thought it was a passage to a hidden room.
Hidden doors -- This company makes cabinets, bookshelves and anything you can think of that fits your existing doorjambs thus hiding the door (and also making use of the space) Not sure I like the idea of a 'gun cabinet' door.