http://www.candlepowerforums.com/vb/showthread.php?384538-4Sevens-Atoms-Family-Review
Last weekend, I spent the night in a hotel. Since I had 2 room keys, and having seem claims that the magnet will not effect credit cards, etc., I left my keys near one of the room keys overnight. The key did not work the following morning.
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Anyone who tells you strong magnets won't affect cards etc is hedging the truth. The magnets are strong, making them useful in holding the lights on metal surfaces [...] If you wish to use the light close to credit cards etc (yes, like on a keychain) perhaps it's best to demagnetize the light using a lighter (as suggested by 4Sevens). Otherwise, I find the magnets useful.
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They look like nice flashlights, but I really don't like the idea of carrying a powerful rare earth magnet in my pocket. Seems like a great way to screw up any card with a magnetic stripe.
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One additional comment about demagnetization: the black residue that appeared on the outside of the light also appeared on the inside of the light. After demagnetization, my light developed some serous reliability issues in terms of mode skipping as well as remaining on when turned on. Cleaning out the inside of the tube with a Q-tip seriously reduced the problem. Cleaning the inside contact surface of the head of the light (which was not on the light during heating, but lubricant may have subsequently worked its way up there) solved the remainder of the issues.