I use earth magnets secured behind my headboard, and under my computer desk. I have one in the kitchen under the cabinet and other rooms of the house. I went to Lowe's and bought magnets. Get the ones that are covered with rubber or some other material that will not scratch the gun. Earth magnets are the strongest and will hold the gun firmly. You will be able to pull it off the magnets if you need it. I use two magnets per gun, one on the front of the slide and one on the rear (especially with polymer frames.)
I had to drill holes in some of them to get the short screws to go through to secure them to the headboard and whereever. This is the best system that works for me. I started with the picture frames that the gun fit into but I never seemed to be near the pictures most of the time. Also, whenever I have pants on I am packing.
Scientist say the universe is made up of Protons, Neutrons and Electrons. They forgot to mention Morons.