# Magnetic Card Readers

**URL:** <https://boards.straightdope.com/t/magnetic-card-readers/304683>\
**Category:** Factual Questions\
**Created:** [May 20, 2005, 2:29am UTC](https://boards.straightdope.com/t/magnetic-card-readers/304683 "2005-05-20T02:29:41Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\
**Post date:** [May 20, 2005, 2:29am UTC](https://boards.straightdope.com/t/magnetic-card-readers/304683/1 "2005-05-20T02:29:41Z")

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While buying some groceries, I swiped my ATM card in the magnetic card reader, only to receive an error message. Tried it a few more times, with the same result. Next, I tried a trick that a clerk in another store had showed me. I wrapped the ATM card in one of the store’s thin plastic bags and swiped it again. Success! My question is, why does this trick work? Usually, any foreign material between a reproduce head and the magnetic media just makes things worse.

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**Author:** ![Queen\_Bruin](https://avatars.discourse-cdn.com/v4/letter/q/e274bd/32.png) [@Queen\_Bruin](https://boards.straightdope.com/u/Queen_Bruin)\
**Post date:** [May 20, 2005, 2:36am UTC](https://boards.straightdope.com/t/magnetic-card-readers/304683/2 "2005-05-20T02:36:19Z")

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I want to know why this works, too. My ATM card has been acting up as of late (gotta get a new one…grrr.)

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**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\
**Post date:** [May 20, 2005, 11:36am UTC](https://boards.straightdope.com/t/magnetic-card-readers/304683/3 "2005-05-20T11:36:03Z")

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There have been several threads on this issue. Try search. I don’t recall that we ever got to a truly expert-who-knows conclusion, but there were some decent engineering theories.