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Stud Finder is a free iOS app that locates wall studs using iPhone's built-in magnetometer, replacing $20–$50 hardware stud finders for DIY tasks like mounting TVs, shelves, and cabinets. It has no subscription, no in-app purchases, and no signup.

Yes. On standard drywall over wood framing — the construction style most North American homes use post-1960 — a magnetometer-based stud finder app locates studs to within about an inch by reading the metal fasteners holding drywall to each stud.

On 1/2-inch drywall over 16-inch-center wood studs, iPhone magnetometer-based detection is comparable to a hardware capacitive stud finder for typical loads (shelves, picture frames, curtain rods, most TV mounts). For heavy mounts above 30 lb, the safest workflow is to use both tools and only drill where they agree.

Any iPhone with a built-in magnetometer — every model since the iPhone 3GS. The newer the phone, the cleaner the signal, but even older devices give a usable reading on standard drywall.

Most plastic, silicone, and leather cases are fine. Thick metal cases, MagSafe wallets and magnetic mounts can interfere with the magnetometer — remove them for the best reading.

Concrete and solid brick walls don't have studs the way drywall construction does, so the app isn't designed for them. For masonry, use the appropriate anchor and a hammer drill.