I bought a stud finder once. The batteries died. I replaced the batteries. It beeped at everything. It beeped at my hand. It beeped at the air. I threw it in a drawer and used a magnet instead. The magnet has never failed me.

The Simple Physics Behind This

Drywall is attached to wood or metal studs with screws or nails. Those fasteners are steel. A magnet sticks to steel. Find the fasteners and you have found the stud.

Stud finders use electronic sensors to detect density changes in the wall. They are fine when they work. But they produce false positives on textured walls, plaster, or anywhere the drywall thickness varies. A magnet cannot give a false positive. It either sticks or it does not.

What Kind of Magnet You Need

A rare earth magnet — the small silver ones, about the size of a watch battery — works best. They are strong enough to grip through paint and a thin layer of joint compound. You can buy a pack of ten for under five dollars at any hardware store.

A regular refrigerator magnet is too weak. I tried. It just slid down the wall sadly.

The Method

1. Hold the magnet loosely between your thumb and forefinger.
2. Move it slowly across the wall in a horizontal line at the height where you plan to hang something. Studs are typically 16 inches apart, so start near a corner or an outlet — outlets are usually attached to a stud on one side.
3. When the magnet pulls toward the wall and sticks, you have found a screw or nail head. Mark that spot with a pencil.
4. Move the magnet up and down in a vertical line from that spot. If you find more screw heads in a straight line, you have confirmed a stud.
5. Mark the stud location and measure 16 inches to either side to find neighboring studs.

When This Does Not Work

Old houses with lath and plaster walls are harder. The plaster can be thick and the fasteners may be deeper. A stronger magnet might still catch, but you may need to tap and listen for the solid sound of a stud versus the hollow sound of the cavity.

Metal studs are actually easier with this method — the entire stud is steel, so the magnet will stick anywhere along it. Just confirm you are on a stud and not a metal corner bead or duct by checking for a continuous vertical line of attraction.