Metal detector
A phone detects metal by watching its compass sensor for distortions in the magnetic field. That works well for iron and steel a few centimetres away, and barely at all for aluminium, copper or gold.
| Sensor used | Magnetometer (the compass sensor) |
|---|---|
| Unit | Microtesla (µT) |
| Useful range | A few centimetres; Earth's field reads about 25–65 µT |
| Cannot do | Find buried treasure, detect non-magnetic metals reliably, or work at the depth a real detector reaches |
The mechanism, not the marketing.
The magnetometer measures the strength of the magnetic field around the phone along three axes. Normally that is dominated by the Earth's own field, which is steady in any one place.
Ferrous metal — iron, steel, anything containing them — concentrates and bends magnetic field lines. Bring the phone near a steel object and the measured field departs from its background value. The tool reports that departure, which is why it reacts to studs, pipes, nails and screws.
What a phone cannot do here.
- This is a magnetometer, not a real metal detector. A purpose-built detector transmits its own electromagnetic field and listens for eddy currents induced in any conductor, which is how it finds aluminium, copper, silver and gold. A phone only listens, so metals that are not magnetic are close to invisible to it.
- Range is centimetres, not the tens of centimetres a hobby detector reaches, because magnetic distortion falls off very steeply with distance.
- Phones contain their own magnets — the speaker, the vibration motor, and very often the case or a magnetic mount. These produce a constant offset and can swamp the reading entirely.
Can a phone really detect metal?
It can detect ferrous metal — iron and steel — within a few centimetres, by sensing how that metal distorts the local magnetic field. It is genuinely useful for finding a stud, a pipe or a nail in a wall.
Will it find gold or coins?
No. Gold, silver, aluminium and copper are not magnetic, so they barely disturb the magnetic field. Finding those requires a detector that transmits its own field, which a phone cannot do.
How deep can it detect?
Centimetres. Magnetic distortion weakens very rapidly with distance, so anything buried more than a few centimetres down is out of reach.
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