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Does a metal detector app on iPhone really work?

Partly, and only partly. A phone metal detector reads the magnetometer - the same sensor the compass uses - so it reacts to iron, steel, magnets and electronics a few centimetres away, and ignores gold, silver, copper and aluminium entirely. In Device Monitor it's the Metal Detector under Environment Sensors, part of Pro.

3 min read · Updated 2026-10-06

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How a cell phone metal detector app works

Every iPhone carries a magnetometer measuring the magnetic field around it in microtesla (μT). The Earth's own field sits around 25 to 65 μT. Iron and steel bend that field, magnets add one of their own, so the reading shifts the moment the phone gets close. That shift is all a metal detector app is actually watching for.

Which is also why it's blind to most precious and non-ferrous metals. Gold, silver, copper, aluminium - none of them are magnetic, so they barely nudge the field. A real metal detector sends current through a coil and induces its own currents in any metal nearby; a phone has no coil, so it can't do that trick.

How to use the Metal Detector in Device Monitor

  1. Open Diagnostics > Environment Sensors > Metal Detector (Pro).
  2. Hold the phone away from metal, tap Start Scanning.
  3. Keep still while it reads Calibrating... hold still - for 3 seconds the app averages 60 readings as its baseline.
  4. Sweep slowly, a few centimetres above the surface. The sensor sits near the top of the phone, so lead with that end.
  5. Watch the μT deviation number and the status word. Past 20 μT the phone taps your hand.
  6. Tap Stop Scanning when done. Start again to recalibrate in a new spot - the baseline doesn't carry over.

What the readings mean

Status by change from the baseline
μT deviationStatus
under 5No Metal
5 to 19Weak Signal
20 to 49Metal Detected!
50 or moreStrong Detection!

A worked example

Say the baseline after calibration lands at 45 μT. Over a steel screw, the three axes read 50, -40 and -60 μT. The total field is the square root of 50² + 40² + 60², which comes to 87.75 μT, so the deviation is 43 μT: Metal Detected!, with a haptic tap. Over a spot reading 20, -30 and -40 μT instead, the total is 53.85 μT and the deviation only 9 μT: Weak Signal, no tap at all.

What it can and cannot find

Realistic expectations
TargetResult
Steel screws, nails, brackets a few cm deepUsually detected
Magnets, speakers, magnetic catchesStrong response
Electronics and power adaptersResponse, which can be mistaken for metal
Gold, silver, copper, aluminiumNot detected
Objects buried in the ground or deep in a wallOut of range
Live cables by their currentNot detected

Tips for better results

  • Take off magnetic cases and mounts, and keep your keys and watch off the phone too.
  • Recalibrate every time you move to a new wall or room - the baseline is only good for the spot you set it in.
  • Move slowly. The reading updates 20 times a second, but a fast sweep can skip right over a small target.
  • Near steel furniture or appliances everything reads high; step away and recalibrate before trusting the number.

Questions and answers

Is the metal detector free?
No, it's Pro only. The free Digital Compass uses the same sensor though, so you can watch it react to a fridge magnet without paying for anything.
Will it find gold?
No. Gold isn't magnetic, so the magnetometer never notices it - same story for silver, copper and aluminium.
How deep can it detect?
A few centimetres for a screw or nail, a bit more for a strong magnet. It's not a ground detector and definitely not a treasure hunter.
Why does it react to my laptop or charger?
Electronics are full of magnets and steel, and current flowing through them creates its own field. The sensor can't tell that apart from a lump of metal.

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