My credit card works fine in most readers, but it seems that when I go to Publix (grocery store chain in my area of the country), their reader has problems. I swipe the card, and I get a message like “Try Another Card”.
The first time this happened, the checkout girl showed me a trick to make it work – which is to wrap a plastic bag around the card (covering the magnetic strip) and swipe it through. It accepted it.
I never have to do this anywhere else, but very commonly at the Publix stores. Apparently this is a trick that all the checkout clerks know. And now I know, too, whenever I’m there.
So, my question? Simply put… Why? Anybody know why wrapping the card in a plastic bag makes the reader take the card, when it won’t on its own?
Crappy readers that get overwhelmed by a strong magnetic signal, perhaps? My WAG is that by putting the bag over the stripe introduces, typically, a 5 mil airgap (yes, I know it’s plastic, but that has about the same permeability as air) that attenuates the magnetic field so that the reader can handle it correctly.
WAG: The slot on the reader has worn away over time, so the card isn’t close enough to the read head when you swipe it through (or it moves closer and farther from the head, giving an inconsistent read). When you wrap a bag around it, the card is pushed closer to the head (or at least stays the same distance away through the entire swipe).
These are not particularly old readers, I think – unless Publix acquired them used. And it’s at more than one Publix store. Just seems to be theirs. Odd.
I guess it’s a common problem with them, though – probably the “Crappy reader” theory from Q.E.D. – since the clerks at Publix all seem to know the plastic bag trick.