Get some 2x4's, plywood, drywall, spackle and paint.
Underneath of light switches (maybe 6 inches down) carefully cut a square hole in the wall a little bigger then the pistol.
build a square with the 2x4's, put a back on it with the plywood and screw it to the same stud the light switch box is screwed to above.
Put pistol and spare (full) mag in a plastic bag. Place in square.
Put a piece of drywall over, covering the hole.
It now looks like the rest of the wall.
Gun is safely hidden, ready to go. Won't be accidentally found by neighbors, visitors, or children.
If you are ever in need, just punch out the wall where you know it is. (trust me, if you need it, punching the wall out will not be a problem) You keep it in the plastic bag so no dust gets in the gun when you punch the wall out.