Can your phone find studs in a wall?

What a phone can sense

Every iPhone has a magnetometer, the sensor behind the Compass app. It measures magnetic fields, and iron and steel nearby bend the field it sees. Apple’s own Compass guide notes that the compass can be affected by magnetic interference (Apple). A stud finder app turns that into a feature: it watches for the bump in the field as the phone passes over steel.

In a typical wall, the steel nearest the surface is usually the screws or nails fixing the wall board to the studs. So a phone can find where those fixings are, and from them, where a stud probably runs.

What a phone can’t sense

• Wood. There’s no sensor in a phone that can see a wooden stud. Dedicated stud finders use different sensors for that.
• Electrical wires. Copper isn’t magnetic, and a phone has no sensor for live cables.
• Copper or plastic pipes. Neither is magnetic.
• Anything far away. The bump from a single screw is small and fades fast with distance, so the phone has to pass very close to it.

How far apart studs are

In the US, the International Residential Code sets maximum stud spacings of 16 or 24 inches, depending on the size of the stud and what the wall carries (ICC, 2024 IRC §R602.3.1). That’s a maximum in a model code that areas adopt with changes, and older homes may differ, so treat it as a hint, not a promise.

What safety bodies say before you drill

These points restate official guidance. Follow the links for the full advice:

• Electrical Safety First (UK) names drilling, nailing or screwing into hidden cables as a common DIY mistake, and says to locate cables first. It notes that buried cables should run horizontally or vertically from sockets and switches, recommends switching off the power at the fuse box, and says a quality cable detector can help track buried cables (Electrical Safety First).
• The Electrical Safety Foundation International (US) advises extreme caution when cutting or drilling into walls, and turning off the circuit breaker before working with wiring (ESFi).

If you’re unsure what’s inside a wall, ask a qualified electrician.

Using The Measure App’s stud finder

The Stud Finder in The Measure App works exactly as described above. You set zero on a part of the wall with no metal behind it, then move the phone slowly; when the line rises above the dashed line, there’s metal, and the high point shows where. The app says on screen that it finds iron and steel only, cannot find wood, pipes or wires, and that you should never drill using it alone.