Best way to detect horizontal vibration/shaking!
Inertial Accelerometers are your friend.

I have recently hooked some up to an Arduino, and here is my writeup of it:

http://hacking.majenko.co.uk/node/32

The ones I have used are ±18g, which equates to ±176.58m/s² acceleration.

With the addition of a capacitor on the output you can reduce the sensitivity to high frequency vibration.