searching for ideas about motion sensing if that's the name

I just drop my laptop by accident, just a couple of feets, it's a Thinkpad T43 full upgraded (memory, hardrive and docking base) , and after a quick survey I found just the plastic bezel sustained some damage, all the rest is working just fine, now, my question is, i heard some macs and other laptops have some kind of motion sense control to be able to sense the fall and park the hardrive plates in case of a fall, my question is: how do you "sense" a falling situation and distinguish it from just a movement? coz a laptop can fall in just any direction, so it looks like more that a engineering problem for me. I will try to keep considering possible solutions for this, although the new "solid state" drives will probably make this post obsolete as soon as they loss some weight in their special price tag .