This application will work only if your mobile have magnetic sensor.
The natural magnetic field level (EMF) about from 42μT - 49μT(micro tesla) or 420mG to 490mG(milli gauss); where 1μT = 10mG. When any metal object like steel, iron is near, magnetic field level will increase.
Not all smart phones have magnetic sensor. Please check your phone specification before using this application. If your device does not have one, the application will not work.