Eli5: When your credit card doesn’t read at a credit card machine, why does covering it with a plastic bag suddenly make it work?

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Had this done multiple time at the register. Card not reading, so the cashier will cover the ribbon or the chip with a plastic bag and YATZEE, it goes through. Why?

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Overtime, some of the magnetized bits on the stripe get what’s called ‘smeared’ out of position. Basically your card gets sloppy. When you swipe the card the reader also reads the smeared parts which present as additional or corrupted signals. When you wrap your card in a bag it creates distance between your card and the reader so the reader isn’t able to read those few bits that have smeared out of position because they present a much weaker signal.

Sometimes it’s the card, as described in the other response. Sometimes it’s the reader itself. When it’s the reader itself, it could be due to having been used hundreds if thousands of times, which not only slowly deteriorates the magnetic reader, but also changes the physical distance between the cards and the reader so that the information isn’t exchanged properly. Next time it happens, try bending the part of the card that isn’t stuck in the machine either up or down (depends on the machine and card). Should be just as effective as the plastic bag trick

the edge of your card wears down so the magnets are out of position. the bag adds onto the edge again and puts the magnet back into place.

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