Why a Magnet Finds Studs When the Electronic Finder Won't

If your electronic stud finder beeps in three places and you've drilled holes in all of them, the people who hang things for a living have heard it before. Ask in r/handyman and the answer comes back over and over. Put the finder down and get a magnet.

Why does a magnet find a stud when the finder can't?

An electronic finder reads the wall from the outside and tries to work out what's behind it. Bob Vila's testers describe them as sensing "changes in wall density", which is clever, and also how it ends up beeping over empty space. A magnet skips the guessing. It grabs the heads of the screws that hold the drywall up, and the screws are in the studs.

Best way I've found to find a stud is a good magnet. Run it along the wall till you find a screw. It's the drywall screws and they are always in a stud.

u/redlightbandit7, in r/handyman

That's the whole trick. The tool is a strong magnet in a small plastic body, and most people in these threads just say "stud buddy", which has become the word for the category as much as a brand. Of the ones who name a maker, the C.H. Hanson magnetic stud finder comes up in three separate places.

In a thread called "Am I just stupid?", one handyman had been through three electronic finders, all worthless, and now uses a magnet and nothing else.

The reply under it is the method in miniature. Run a dozen tiny rare-earth magnets over the wall, leave each one where it sticks, and before long you've mapped out how the drywall was hung and know where everything can go.

How do you use a magnet to find a stud?

The handymen in these threads don't drill on the first grab. The order is the same from several of them, and it's quick.

• Knock first. One handyman threw the electronic finder away after a few false readings and knocks instead. The sound goes duller over framing and hollow in between, and that gets you close.
• Then slide the magnet. Sweep it slowly across that patch of wall. When it grabs, it has found a screw head, and the screw is in a stud. Leave it hanging there.
• Check sixteen inches over. Studs sit sixteen or twenty-four inches apart, centre to centre, and one reply's rule is to check that distance over to make sure you've found a layout stud and not a patch or an oddball.
• Map the screws, not just one. Drywall screws run in a line up each stud. Find two or three on the same vertical and you have its direction as well as its position. A skylight installer who has to know which way the trusses run puts three stud buddies on at once, for direction, location and spacing.
• Mind the edge. A screw can sit off centre, or go into the stud at an angle. One commenter has come off the edge of a stud that way, so once you've found the line, aim for the middle of it.

Should you throw the electronic one away?

No, and plenty of the people who love the magnet still keep one. The pattern that repeats is the electronic finder first for a rough idea, then the magnet to prove it.

I use a Franklin, then a Stud Buddy. Works every time. No need to drill holes to verify.

u/Alert_Reindeer_6574, in r/handyman

Franklin is the electronic brand these threads name when they name one, and on Garage Journal the model that keeps coming up is the ProSensor.

Elsewhere in the thread it's a stud finder and then a stud buddy to confirm, or the magnet as the main tool with the electronic one out only for triple-checking where the AC power is.

That last line is the limit. A magnet finds screws, not wires or pipes. Bob Vila's roundup credits the electronic finders with detecting pipes and wiring, and that's the job the magnet can't take over.

On the Garage Journal forum, a member runs a Franklin and keeps the Hanson for the parts of the house where the plaster is too thick for the electronic one to read.

Bob Vila's roundup, four electronic picks and one magnet, calls the Hanson an excellent backup for an electronic finder. The handymen would put it the other way round, but the pairing is the same.

Does a magnet work on plaster walls?

The threads argue about this one, so you get both sides.

In one thread, a commenter says the magnet doesn't work that well on plaster and lath. The reply under it says it does, and that it was the only way they found the studs in their house from the 1920s.

Two more say it only works on drywall. In lath and plaster the nails sit too deep and too small for a magnet to feel. With plaster, the other says, you're out of luck.

On Garage Journal, a member with a 1950 house, drywall then mortar then plaster, found the nails too far below the surface as well.

Every no that comes with a reason gives the same one: the nails sit too deep. The ones who say yes don't say what made their walls different. The only way to know which you've got is to slide a magnet over it, and one costs little enough to find out.

One more plaster trap, from Bob Vila: because a magnet detects metal rather than the stud, it can grab any metal in the wall, and old plaster is sometimes held on by metal lath. A grab that doesn't repeat sixteen inches over isn't a stud.

What if the magnet finds nothing?

The person who asked "Am I just stupid?" had tried a magnet before drilling, a big fishing magnet, and it found nothing either. Later they bought a new electronic finder. On another wall it found a stud straight away, and on the TV wall, still nothing. A wire pushed in through the drill holes didn't touch anything. Their own guess was that "someone did something weird" when the house was built.

The replies had a few suspects. Over a fireplace, or where an old window or door was closed up, the framing may not follow the usual layout, and one wall turned out to have horizontal wood closing an old opening. Another house had plasterboard glued straight onto block with massive dabs of adhesive, and both the finder and the knock test read the blobs as studs.

If a magnet goes over the whole wall and never grabs, more holes won't help. That wall isn't built the way the method expects.

Which magnet?

The magnet matters less than the method. The dozen loose magnets from earlier do the job, and so, one reply says, does a bare neodymium magnet picked up cheap. Three made-for-the-job ones come up by name.

• The C.H. Hanson. It has a bubble level and a loop for a plumb bob, and a handyman who'd been through "three of the electronic frustration machines" is content with it. Stubborn Gear, a small independent test site, ranked it the best stud finder of everything they tried, electronic ones included, because it doesn't give the false readings the electronic ones do. On Bob Vila's test wall it stuck to the drywall by itself over a fastener. Another handyman keeps ten or so scattered about the place.
• The Original StudBuddy. A different product from a different company, whatever the threads' habit of using its name for all of them. Stubborn Gear ranked it second, similar in function to the Hanson but with smaller magnets. If you'd rather have the StudBuddy, nothing in the method changes.
• The StudPop. A third make. A Garage Journal member bought it over the others because it's small and needs no batteries, so it lives in the tool bag.

Get the Hanson three-pack, since the method wants more than one magnet on the wall. Knock first, slide the magnet until it grabs, then find its neighbour sixteen inches over. The electronic finder goes in the drawer, and comes out the day you need to know where the wires run.