Hereâ€™s a cool toy app created by 6Fg8, a member of XDA-Developers.com.
The software for the HTC HD2 uses the built-in compass to detect metal nearby by the deviation of the earthâ€™s magnetic field included by the metal.
How to use:
Place your device flat on a surface. After starting the app, the gauge should show zero. If it doesn’t, take your device and write a couple of "eights" in the air (this is to get rid of magnetism which might get stuck in the sensors).
Then use a pair of scissor or something the like and move it slowly to the right side of your device. At a distance of approx. 5 cm. the gauge should start to move. Take your device and move it with its right side near metals, and see if the gauge shows values.