What is magnetometer sensor in mobile?

What is digital compass (magnetometer sensor) in mobile? 

Digital compass 

Digital compass (magnetometer sensor)  that's usually based on a sensor called the magnetometer and provides smart phones with a simple orientation in relation to the Earth's magnetic field. From the digital compass to find out what is the direction of East, West, South and North. Your phone always knows which way is North, so it can automatically provide directions your digital maps depending on your physical orientation.

How it's works magnetometer sensor (digital compass) in mobile. 

The compass of our smartphone is quite similar, counting with three axes (X, Y and Z) that are sensitive to the Earth's magnetic fields, and move accordingly to these magnetic fields, being able to signal our orientation with respect to the Earth's magnetic field.

Magnetometer sensor 

They can make the magnetometer respond to metals such as nickel, iron and steel, and it could be useful to determine if there are wires behind a wall or even to find lost objects behind the bed. which is why you can get metal detector apps for your smartphone.