It should be fine, metal detectors arent strong enough to emit a pulse strong enough to erase a hard disk. If they were people would be complaining at airports all the time. The frequency is just strong enough to detect metal-like objects. Anything else would have to be x-rayed, and those are harmful to hard drives... But you won't be exposing your harddrive to x-ray's now are you? :P
thanks guys... never really occured to me that it would probably set the metal detector off anyways :D guess I'll be playing it safe like i've been doing for some time now haha.