[ryan-c]

I've seen card readers try to read from both sides of the card in case it's swiped on the wrong side - you might have some problems with those.

[christiangenco]

For compatibility, penny will offer a special adapter that will decrease interference with some card scanners.

You can purchase this compatibility adapter for $3.95 for 66 feet: http://www.amazon.com/Scotch-Electrical-75-Inch-66-Foot-0085...