If you are fortunate enough to possess a MacBook or MacBook Pro, SeisMac is an application that takes advantage of the motion sensors included within these laptops and converts it into a real seismograph.
The movement that is sensed by the computer is represented by three graphs that correspond to different spatial coordinates: horizontal displacement (X axis), vertical displacement (Y axis), and depth (Z axis).
It is not necessary to have an earthquake to test the functionality of this program. Simply move it close to a loud speaker or hit or shake the table, and watch the graphics evolve.
SeisMac lets you review the complete history of the session to see if there was an incident, and if so, find out when it happened. Also, it is possible to select the frequency of updates and the magnitude of the values represented by the application.