This is a make-it-yourself version of a pair of popular products that add magnetic keyholding to a common light switch plate.
Keyholders are pretty utilitarian, so they're a common target for designers who want to add a bit of flair. And magnets have a bit of natural magic about them. Since keychains usually have at least a bit of ferromagnetic metal in them, magnetic keyholders are common and plentiful. And since grabbing the keys and turning off the lights often happen at the same moment, putting your keys on a light switch plate is a natural pairing.
There are two different products out there that do that. One hides magnets behind the switch plate, adding an invisible feature to a common household item. The other replaces one of the screws on the plate with a magnet/screw combination.
Plastic switchplate, whatever number of switches (or "gangs") matches where you want to hang your keys. (Metal plates ones can interfere with the magnet, wooden ones are often too thick for magnets to work well through.) Get an oversized one if you can find them. The larger size will keep the keys from rubbing on the wall.
Rare earth (neodymium) magnets. One (or more) for each keyring you want to hold up. I'm using magnets salvaged out of a hard drive because they're thin and powerful (and free) but any 3⁄16" (5mm) or thinner should work. If you're buying magnets, get a pull force as large as possible.
Scrap paper and disposable sticks for mixing epoxy.
Optional: latex/nitrile gloves because getting epoxy on your hands is no fun.
Safety note: Rare earth magnets hide a lot of power in a small size. Even small ones like we use in this project can unexpectedly attract, pinching or even break the skin. Avoid putting yourself between any two magnets.
Make sure your magnets will hold your keys. Put your magnets one side of the switch plate and the keys you want to hold on the other and lift it up. The magnet should easily hold up they keys. Give them a pull and make sure they'll attach easily. If not, try orienting the magnet differently, or using more than one. (Magnets are weird. Doubling the number of magnets will not necessarily double the holding power.) And of course make sure there's ferromagnetic material in the keys.
Also be sure the magnets can fit on the inside of the plate without sticking above the rim or the plate won't fasten securely against the wall.
Clean and dry both the magnets and the inside of the switch plate. Mix a small amount of epoxy according the instructions and apply it to the back of the magnets and hold them in place with nylon tape. The tape is particularly important if you're using more than one magnet (like mine) to keep the magnets from moving toward each other before the epoxy cures. It's also a layer of safety that falls under the "Not really needed, but why not?" category. Magnets are conductive, switch innards are conductive, and mains current flows through the switch. There is virtually no chance that the magnets will short out anything, but the tape makes doubly sure.
After the epoxy fully cures (Not just sets. See the instructions for your epoxy.) install the new switch plate, and stick your keys in their new home.
Optional: 6-32 nuts, 4 for each screw to help protect the screw heads.
Fine grit (~150 grit) sandpaper rated for metal.
Optional: latex/nitrile gloves because getting epoxy on your hands stinks. The chances of getting it on your hands with this project is pretty high. And once it gets on your hands, it gets on everything you touch.
Well, yes, but it's not great. Rare earth magnets are brittle, crumbly, and rust quickly when exposed to air, reducing their effectiveness. That's why they're usually covered with nickel. (Also because it makes them look shiny and not brown and sad.) Drilling a hole in a magnet pierces this protective shell, and the inside is very likely to crack and crumble. It will also heat the magnet which will reduce its strength. So you can drill a hole in one. But don't.
Like above, make sure your magnets can hold your keys. I'm using a group of four square magnets because that's what I had on hand. A single larger one would work better. (Though a square shape makes it easier to screw in.) If you're combining magnets like me, try different orientations to make sure you get the most stable, strongest arrangement.
In the US, switch plates are attached with 1⁄2" long 6-32 oval head machine screws. The oval head is bad for gluing since it doesn't have a flat surface and is usually covered with paint. So we're replacing them with steel flat head screws. I chose Phillips head because the star grooves give more surface area for the epoxy to grip, but straight will work too.
Even steel screws have an anti-rust coating, so rub the flat head on some sandpaper to remove it. (And provide a rougher surface for the epoxy.) If you want to use pliers to improve your grip, thread nuts onto the screws to protect the threads.
Also rub the back of the magnet on the sandpaper. (Sticking some masking tape on it can make it easier to hold.) Don't rub too hard or too much, just roughen the surface. Rare earth magnets are naturally very brittle and are covered in a protective metal coating. We want to roughen it the coating, not remove it.
Clean the sandpaper residue off the screw and the magnets, and make sure they're dry.
Mix up a small amount of epoxy according to the instructions on the package and apply it to the screw head. Stick the magnet to the screw. The magnetic attraction between the two parts should hold it in place. (But can also snap it into a place you don't want. So be careful.) Wipe away excess epoxy.
Step 4: Install and enjoy.
Wait for the epoxy to cure completely and replace some of the screw on your wall plate with the new screws. (I removed the white screws from the top of this plate and replaced them with steel ones so they'd match the look a bit better.) Use your fingers to tighten the screws. If you have a hard time getting them to thread, use the original screws to chase the threads in the switch and/or some 6-32 nuts to chase the threads on the screw.
Epoxy is strong, and the new magnetic heads will handle the stresses of attaching/removing keys well, but they don't love twisting, so don't go crazy with the torque when screwing them in. You shouldn't be able to break them with your fingers, but you might if you get wrenches involved.