We live pretty close to the rail tracks, and for a long time I wanted to create a system that is capable of measuring the vibrations of the trains passing by. I tried to do it using the Sudden Motion Sensor built into an old MacBook Pro, but I don't think it correctly detects the type of frequency caused by trains passing by.
Also, a MacBook Pro is not exactly the type of hardware that you would use to put sensors in multiple places. ;) So I'm wondering if there is a (hopefully) USB device or some other device that I can connect to my Pi to measure what's happening.