years ago, a friend that was a registered locksmith and safe technician was building his "gun room"... his comment to me was that if it was "in sight" it could be opened..... he built his into the cedar closet, utilizing a magnetic switch to activate a solenoid that would release the lock mechanism... all he had to do was to place a small powerful magnet to a particular place on the wall of the cedar closet, and the wall mechanism would pop open...
another friend had an 6' deep room the width of his den... the entire wall was overlapping cedar shake shingles... the texture cleverly camouflaged the door... the wall studs had galvanized 1/2" pipe running horizontally every 10 or so inches... inside each pipe was a two foot section of cold rolled steel, separated by a marble...the object was that if it were attacked by a hacksaw or chainsaw, the inner piece of cold roll would spin, and not allow the blade to get a good bite