I always use my Amex card for groceries to build up frequent flyer points but the card is getting a bit long in the tooth. When I swipe the bare card it almost invariably fails to read but if I wrap it with one of those thin plastic bags it almost invariably works. This flies in the face of any law of physics I ever hear of. A thin polyethylene film should not have any effect on a magnetic field.
Why does it work???
Glenn,
Two things spring to mind. First, it might be restoring an inert spacer that is wearing off of your card. I have NO real clue about magnetic strips, but have always appreciated the strong spatial variations in magnetic fields. It might be important to "stand off" some to get a reasonable reading.
Perhaps more likely: you know the card is worn, so you might be (as one of my horsemanship mentors would say) candy assing it [*] when it's not covered. To be fair, you would have to blind yourself to the covered/uncovered status.
[*] sorry, but if you knew her, you'd understand just how well that fits.Bill
Googling "credit card magnetic plastic bag" yields a number of discussions which support this view--may be that the card is going or it may be that the readers are misadjusted but one way or another a little more distance between the stripe and the head seems to make the difference. One fellow claims that he can make his card read or not read depending only on which side of the slot he presses it toward.
FWIW, this is something so commonly known among sales clerks and seems to work reliably enough that it would seem to be a physical phenomenon and not psychological.
One fix for this is to put a piece of scotch tape over the strip. Do it when it's new and the strip will last a long time. However there are some readers which won't like the tape. As for why it works I'm not sure but one theory I've heard is that the rough strip prevents smooth swiping of the card. The plastic allows for a even swipe.
Wayne Cook Shamrock, TX
Maybe it's just dragging the accumulated crud off the read heads?
The last time I was at Harbor Freight, the clerk did this with my card. He tried it normally first and it wouldn't read. I have seen all kinds of thinks done to cards to get them to read, including spitting on the card and then wiping it off on the clerk's jeans!
The same card works everyplace else, so the problem has to be in the reader, itself, not the card.
Paul
Smooths out the head bounce.
DMaybe it is placement. Further from the reader. Less noise from a noisy card. As a card is used it gets noisier - magnetic fields and metal - all bring in noise that finally makes the signal fuzzy. At a distance, the fuzz is 'toned down' and the stronger lines come through.
Martin
Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder
Glenn Ashmore wrote:
As I tell the cashier at the grocery store "it's all in the way you cross your toes." Gerry :-)} London, Canada
Newer cards have a higher strength mag material and this will overload some older readers.
The plastic will reduce the signal strength.
Some new cards have a protective layer over the mag stripe that will wear away and this causes an increase in the signal strength.
Hugh
Mart> Maybe it is placement. Further from the reader. Less noise from a > noisy card.
Newer cards don't have a stripe. It is a metal 'shield' and a u processor inside running Java.
Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder
Hugh Prescott wrote:
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