MAG3110 Magnetometer Hookup Guide
Aside from sensing magnetic north, this sensor has a few other uses. Many high power electronics create magnetic fields of their own. With this sensor, you can see this disturbance.
An example sketch is included with the library called
SparkFun-MAG3110-Magnitude.ino. This sketch first calibrates the sensor and then outputs serial data of the magnitude of the scaled x and y-axes. Recall the magnitude of a vector is:
In this case a3 is 0 since we do not take the z-axis into account.
Once the sketch is running and calibration has completed, open up the Tools->Serial Plotter in the Arduino IDE (only available in the newest versions of the Arduino IDE). If you put the sensor near a microwave and then warm something up, you will see some noise on the signal.
And, if you put a fridge magnet near the sensor, you will see large spike! Be careful though, the sensor has maximum limits of magnetic field strength it can be exposed to without damage.