Metal Detector - Magnetometer EMF - measure magnetic field value using a magnetic sensor that is built into your smartphone.
Now You can easily find metallic objects that are hidden underground, behind walls etc. , or be a treasure hunter or ghost hunters, also see a reading trend through the graph.
Simple app in your device called Gauss Meter are used for measuring the Earth's magnetic field but can't detect silver, gold, copper coins (non-ferrous - no magnetic field).
This Magnetometer app require a magnetic sensor otherwise does not work.