Monday, August 25, 2014

Can you find a hidden hard drive with a compass?

I finished Season 4 of 24 yesterday. In one episode a hiker found a tiny radio transmitter under the leather of a briefcase with a compass. Then in a later episode the baddies trashed an apartment looking for a hidden portable hard drive. There's very strong magnets in a hard drive. Couldn't a compass reveal those fields? Could they have used the compass trick to find the hard drive? 

It was easy to put my hands on my compass and a portable hard drive so I tried it out.

The compass definitely jumped all over the place when I put it near the hard drive. But it has to be REALLY near it.

Compass held above the hard drive so it points
to natural North. 
This is how close I had to get before it moved
the needle significantly.
So if you cram a hard drive between the cushions
of your upholstered furniture nobody will find it
with a compass.
Of course while I had the compass out I had to see what other stuff did. The steel legs on my glass table made the compass go mad. My 27" LCD monitor made it jerk wildly. My large loudspeaker makes a very nice magnetic field. As I was playing with the compass by the speaker it occurred to me my Mac mini is in that same spot on the other side of the speaker, in a strong magnetic field.
Hmm. That's a magnetic field.
And here.
Up above the speaker is where it should point.
I moved the speaker and moved the compass around the computer. Much less deflection of the needle. The high end driver of that speaker is a horn. The compression driver has a strong magnet quite close to where the Mac mini is. The midrange driver magnet is about the same distance the other direction. 

But so what? Well, so what nothing. It's just interesting. Modern hard drives are virtually immune to normal everyday natural magnets. Besides, erasure requires a hard drive to MOVE THROUGH a magnetic field to reverse the polarity of the magnetic particles on the platters. And as you can see by the pictures, the field drops off quickly with distance. I'd need to rub the biggest speaker magnet I've got right on the case of the hard drive to have a chance of erasing it. And it probably still wouldn't count. The computer performs just fine in this magnetic field. 
Here's a piece of art I made out of hard drives from work I was told to destroy.
Several parts spin.
This was at my old place in Austin. I hinged the frame of the picture to reveal
the original wallpaper that was under the top layer I peeled off. It was stuck on so good
I just painted over it. When I moved out I gave the art work to a friend
and painted the remnant. Too bad.
For more fun with a compass I recommend running it over your iPad. It clatters around like mad. Very strong magnets in the smart cover.

*In case you missed it, Can you find a hidden hard drive with a compass? No. But you can have fun.

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