If you ever wanted to play around with a earthquake detector, this system look quite simple and well documented.

“Let me admit at the outset that due to a scandalous absence of earthquakes in Northern Ireland this project has never been tested on any meaningful earth-movement whatsoever. However, the setup is sensitive enough to detect passing cars, bad-tempered neighbours slamming doors 10 metres away and pile drivers at a distance of more than a mile.

Most earthquake detectors use a heavy weight attached to a coil moving inside a magnetic field. Earth movement will cause the ground and attached magnet to move. The suspended weight and coil tend to stay stationary and hence a signal is generated. Elaborate electronic filters and damping needs to be employed to get a meaningful signal. ”