DrDaq Earthquake sensor

Are there any information on making, or buying, a low cost earthquake sensor I could use with my DrDaq?

Only one I have seen is in a radioshack book. It was a long tube (3 feet) with a suspended magnet over a hall sensor. Tube was screwed to the bed rock and I think the magnet has to be heavy to avoide being effected by the earth's magnetic field.

I use piezo electric transducer connected to the scope input of DrDAQ. You can also connect the piezo transducer to your computer (line in or micro input) and use Audacity (for example). I can give you more details for the second solution (in french but with full pictures). Sorry, I don't speack english very well

I use the USB DrDAQ to measure "seismic waves" and simultaneously measure the stresses acting on the "fault". You will find all the details here (in french, sorry!) : https://sites.google.com/site/desideesp ... ontraintes
You have to download the pdf file named "enregistrer les contraintes et les ondes"