How a stud finder app works on iPhone

Your iPhone already has a magnetometer — the same sensor the Compass app uses. A stud finder app like ours watches for magnetic spikes from the screws and nails that anchor drywall to each wall stud, then shows you where to drill.

The sensor you already have

Every iPhone from the iPhone 5 onwards ships with a three-axis magnetometer. Apple uses it for the compass and for augmented-reality heading. We repurpose that same chip to measure tiny magnetic disturbances in a drywall surface — the ones created by the steel screws and nails driven into the studs.

A standard wall has a stud every 16 inches (or sometimes 24 inches). Each stud is anchored to the drywall with several fasteners. The app does not detect the wood itself; it detects those fasteners. Because the fasteners sit within an inch of the stud's center, finding them is close enough to mount safely.

Step-by-step: how to use the stud finder app

Tips for an accurate reading

• Hold the iPhone flat against the wall. Even half an inch of air gap weakens the signal.
• Sweep slowly — no faster than a few inches per second.
• Scan from both directions and mark where the peaks line up. The center of the two marks is the stud.
• Remove MagSafe wallets, magnetic cases, and metal kickstands. They confuse the reading.
• If the wall seems dead, try a spot near an outlet box. Outlets are almost always mounted directly to a stud.

When a stud finder app is the right tool

For hanging pictures, shelves, curtain rods, and most flat-screen TVs on standard drywall, a phone-based stud finder app is reliable, free, and always with you. For very heavy mounts, plaster walls with metal lath, or commercial steel-stud construction, combine the app with a hardware capacitive stud finder and drill only where both agree.