Detect-O

Detect-O is a Metal Detector application for the iPhone 3GS. It uses the magnetometer to detect the presence of nearby ferrous metals.

Due to the way the magnetometer operates, Detect-O will register changes in the nearby metals, but will not indicate a steady reading with nearby metal; rather, it will register when approaching it and when leaving the vicinity of the metal.

Also, since Detect-O operates based on magnetic slew rate, it may give false readings if the iPhone is rotated rapidly or otherwise changes headings rapidly.