Choose the site of your hidden gun safe carefully. The wall of your master bedroom would be ideal because hiding your gun in your bedroom offers maximum security due to its accessibility. When you have decided the room in which the safe will be hidden you need to choose exactly where on a wall it is going to be placed. Around shoulder height is good because that is a height at which another object, such as a picture, can act as a cover, and because you can access the safe without having to stretch. The safe will need to be secured to the studs of the wall, so locate them by either using a stud finder that you can buy at your local hardware store or by tapping the wall with your fingertips and listening. The space between the studs will sound hollow.
Mark an area on the wall in pencil that spans the distance between the studs and that will be large enough to accommodate your gun. Use the reciprocating saw to cut out the area that you have marked out.
Cut pieces of 2 inch x 4 inch lumber that are wide enough to span the distance between the studs and as long/tall as the longest gun that you want to secure in this location. Screw the pieces of lumber into position to form the frame of your safe.
Cut a piece of hardwood board that will cover the frame that you have made. This will form the door of your safe. Install a hinge 2-3 inches from the top and the bottom of one edge of the door and attach to the edge of the frame so that the safe is enclosed.
Secure the lock hasp to the other edge of the door.
Hide the safe by hanging a picture or mirror over it. The picture or mirror will need to be several inches longer and wider than the frame of the safe so that it remains hidden.