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Faulty Debit cards

  1. Jul 19, 2005 #1
    Could someone explain why putting a shopping bag over a debit car make it readable for the scanner? I've always wonder why this is, and I'm almost certain it has to do with physics.
  2. jcsd
  3. Jul 19, 2005 #2


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    I've never heard of that trick, but I know of a few instances of cellophane tape being applied. From what I've seen, the fault usually lies in the reader, not the card itself. Cards work some places and not others, so I suspect that some readers have more discrimination than others and are more sensitive to imperfections. I thought that the tape might help to stabilize micro-fractures in the magnetic material, but a bag wouldn't do that. Maybe it just covers surface irregularities that would cause the card to 'skip' a bit due to uneven contact with the reader slot.
  4. Jul 25, 2005 #3
    The magneitc stipe must be very close to the scanning head to make
    a successful read. Even a bag's thickness is too far away.
  5. Jul 25, 2005 #4
    No this happens to me quite regularly. My card works everywhere except at the 7/11 just down the road. Everytime I go there the guy behind the counter gets a plastic shopping bag, puts it over my card and presto, it goes through. I don't have any idea why, but this trick certainly does work.
  6. Jul 26, 2005 #5
    Oh I see. I had it backwards.

    It's likely that there are low-level magnetic errors creeping onto the
    stripe which is fooling a sensitive reader. By reducing the strength of the
    signal, only the main encoding is detected.
  7. Jul 26, 2005 #6
    Did you hear the one about the experimentalist who compiled his recent data in graph form to show his more theoretically inclined colleague?

    The theoretician said ''this data makes perfect sense...we would expect to see that hump there....and that flat section is right where it should be....".

    The experimentalist says "Oh dear, that graph is upside down, let me help you orient it". Without skipping a beat the theoretician continued "...and this concave region is just what we would expect from..." :smile:
  8. Jul 27, 2005 #7
    I haven't heard the joke but I've lived it more than once!
  9. Jul 27, 2005 #8
    I use a card scanner in my shop, and was told by the company, that the plastic evens out the strip. They told me it has to do with the manafacter of the cards, some just wear better then others. I have noticed that to be true.
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