Modern iOS and Android smartphones contain a large number of sensors that work in the background. One of them is the magnetometer: the sensor responsible for the digital compass. It measures the strength of the Earth’s magnetic field along the X, Y and Z axes and determines the orientation of the device based on this, which is used by applications such as Apple Maps and Google Maps.
The Earth’s magnetic field is stable in the short term, so when the phone approaches a larger object made of metal containing iron, the magnetometer registers a sudden jump in value. It is precisely this jump that the applications interpret as the presence of metal near the phone. Because of this, some applications may vibrate or show a sudden increase in readings when the phone is near a metal object.
However, the phone is technically not a real metal detector. Classic metal detectors actively send electromagnetic pulses and measure their attenuation or return signal, while the magnetometer only passively records disturbances in the existing magnetic field. Therefore, smartphones cannot detect non-metals or small objects, nor non-ferrous metals such as aluminum or copper.
MUOIn practice, this kind of “detector” reacts best to larger objects with strong magnets, such as speakers, headphones or large electronic devices. Smaller objects, such as a metal pencil, often remain below the detection threshold.
Among the applications available, most specialized metal detector tools offer limited accuracy. A much more useful solution is the Physics Toolbox application, which graphically displays changes in the magnetic field over time and along all axes, which allows for clearer observation of anomalies and a more realistic insight into the operation of the magnetometer.
The conclusion is simple: the phone can “sense” metal nearby, but this should be seen as a side effect of the compass, not a replacement for a real metal detector, writes MakeUseOf.