Equipment/V91 Degausser
From London Hackspace Wiki
Safety
This machine generates a very high intensity rotation magnetic field in order to erase hard drives which will also cause damage to watches, phones, laptop screens etc. that are nearby so please use this device with extreme caution in an isolated area away from all other electronics.
Video
A hard drive being erased: http://www.youtube.com/watch?feature=player_embedded&v=YLDA_kFItKU
(spot the obvious mistake, I don't think he should be wearing that watch).