Magnetometer lets you view current electromagnetic fields around you! To use, simply open Magnetometer and bring your iPhone close to any ferromagnetic metal such as iron or steel, or any other magnetic object. Magnetometer will measure the current magnetic fields on the X, Y, and Z axis in micro-teslas. In addition Magnetometer displays a magnitude reading of (X^2+Y^2+Z^2).

Here are some practical ways of using Magnetometer:

Metal detector: Imagine yourself buying some gold coins. By using Magnetometer you could tell if they were real or fake by holding the coin up to your iPhone. If the magnitude goes up dramatically, you can be sure that the coin is fake.

Educational purposes: You're sitting in science class and the teacher starts talking about electromagnetic fields. Impress your teacher by showing them your fully portable Magnetometer on your phone! Use Magnetometer in various science experiments while your fellow classmates watch you in disbelief.

Ghost Hunting: Use Magnetometer like a real EMF detector! A very common theory is that ghosts disrupt magnetic fields, thus a person can find ghosts by viewing disturbances in magnetic fields. Whether you're a professional or an amateur, Magnetometer is the app for you!

How exactly does it work?
Since the iPhone 3GS/iPhone 4 includes a compass, Magnetometer can measure the interference created by a ferromagnetic metal (or paranormal activity). Magnetometer is NOT a true magnetometer and shouldn't be used for anything but entertainment purposes.