Magnetic Fields change when near metal, using your phones magnetic field sensor, you can find hidden metal objects, or metal wires running through your walls.
Some phones may be more sensitive than others depending on the quality of it's sensor.
Move your phone around and watch the numbers change, sensors can also be affected by TV's PC's etc.
If you have a leather or plastic case for your phone that has any metal or magnetic clasps, remove the phone from the case to get a more accurate reading.
Have fun detecting metal – download Metal Detector today!!!