"Metal Detector Professional" uses built-in magnetic sensor to find metal objects.

How it works?
With the use of magnetometer our tool measures electromagnetic field (EMF) value in your surrounding. Actual value of the field is displayed as microtesla. Induction of Earth's magnetic field ranges from 30 to 60 microtesla (µT). If the intensity increases above 60 µT it might mean that the telephone is near to ferromagnetic materials (metallic objects). Having such information you can try to find wires in the walls and metallic objects under the ground.