Jochen’s DIY earthquake detector made from old hard drives – “…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. My project avoids some of these problems by the use of ready made detectors with a low impedance and their own built in damping.” [via] – Link.