>>I would be concerned with any permanent magnet. Try passing a compass near and around the devices to see if it upsets the compass.
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>Yes compasses are natuarally affected, but what is even more fun is to move the device close to a CRT monitor it does not pretty phsyadellic stuff to the display :)

There's a story about a guy who carried a pack of important floppies (5.25 at the time) in a trolleybus and took care to keep them above the crowd, so they don't accidentally get bent too much. But the transformer was on the roof, just 25cm above his hand. They were low-level formatted.