Remember that black tweeting apparatus security guards use to scan for metallic objects? Its called a metal detector for obvious reasons, its actually based on the concept of inductance.
The inductance of an inductor is dependent on the permittivity of its core; by changing the composition of the core one could change the inductance of the inductor. Its from this concept that Bruno Gavand based his version of a metal detector using a PIC12F863 and a 330uH ferrite bead he calls it the picoDetector. The picoDetector’s firmware was written in C using Microelectronika’s MicroC Pro and is compatible with most PICs.