Bart Bervoets wrote:
Is it possible that inside certain harddisks motion detectors are placed?


Yep, many do, to prevent head crashes when the drive gets jostled. Get
the drive model number and look up the manual on the Internet (a set
of tubes). It's there plain as day.

As a side effect, it turns out to be quite possible to set up an ad-hoc
earthquake monitoring network, just with a little added software!
Very clever!