Stud detector: what it does and when to reach for it

Learn to use a stud detector correctly, understand its limits, and check for cables before drilling any wall.

SD-01Understand what the tool actually findsA stud detector (also called a wall scanner) is a handheld device you slide across a wall to find what's hidden behind the plasterboard or plaster: timber studs, metal fixings, and sometimes electrical cables or pipes. Cheaper ones only sense density changes (good for studs), while pricier ones add a separate 'live wire' mode using an electrical field sensor. Know which type you have, because a basic model will not reliably spot cables at all.

SD-02Calibrate it on a known-safe patch firstHold the detector flat against the wall in an area you're fairly sure is just plasterboard, away from sockets or switches, and press the calibration or reset button as instructed by the manual. This tells the device what 'nothing there' feels like electronically, so it can spot changes accurately. Skipping this step is the most common beginner mistake and causes false readings later.

SD-03Scan slowly in a straight lineMove the detector across the wall at a slow, steady pace, no faster than about 25mm per second. Watch for the light or beep to change, which signals an edge. Beginners often swipe too fast and miss the signal, or stop the moment they hear the first beep instead of finding both edges of the object.

SD-04Mark both edges and find the centreWhen the detector signals a change, mark that point lightly in pencil. Scan back the other way to find where the signal changes again - that's the other edge. The middle point between your two pencil marks is the centre of the stud or object, which is where you'd normally want to drill or fix.

1 each · Pencil

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1 roll · Masking tape (for marking without marking paint)

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SD-05Do a second pass at a different heightRepeat the scan about 200mm above or below your first line. Studs and cables run vertically or horizontally in fairly predictable patterns, so a second reading in the same spot confirms what you found isn't a one-off glitch. If the two scans disagree, trust neither, and treat that section of wall as unknown.

SD-06Know what the detector cannot promise youBefore you drill or cut into any wall, treat it as if a cable or pipe is behind it and prove otherwise, rather than assuming it's clear because the detector said so. Detectors can miss cables that run deep, sit inside metal conduit, hide behind metal-backed plasterboard, or simply don't follow the 'safe zone' pattern - this is especially true in older houses or where a previous owner did their own wiring. If there is any doubt at all, isolate the circuit at the consumer unit (the fuse box) before drilling, and turn off the water at the stopcock before cutting into anything that could carry a pipe.

SD-07Check you've got it right before committingPush a bradawl (a small pointed hand tool) gently into your marked centre point rather than going straight in with a drill. If it meets firm resistance evenly across a few millimetres, that's timber, which is a good sign. If it slides in freely or hits something hard and metallic-feeling, stop and reassess rather than drilling on regardless.

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