# credit cards

**URL:** <https://boards.straightdope.com/t/credit-cards/43543>\
**Category:** Factual Questions\
**Created:** [December 1, 2000, 6:44am UTC](https://boards.straightdope.com/t/credit-cards/43543 "2000-12-01T06:44:48Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Ptrinsey](https://avatars.discourse-cdn.com/v4/letter/p/7ab992/32.png) [@Ptrinsey](https://boards.straightdope.com/u/Ptrinsey)\
**Post date:** [December 1, 2000, 6:44am UTC](https://boards.straightdope.com/t/credit-cards/43543/1 "2000-12-01T06:44:48Z")

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Why can’t I put my credit card on that scanner that says I can’t? In a clothes store for example.

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**Author:** ![siva](https://avatars.discourse-cdn.com/v4/letter/s/7c8e57/32.png) [@siva](https://boards.straightdope.com/u/siva)\
**Post date:** [December 1, 2000, 6:47am UTC](https://boards.straightdope.com/t/credit-cards/43543/2 "2000-12-01T06:47:42Z")

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if im thinking of the scanner that your talking about its because it is magnetized. credit cards may not work again if that strip on the back is close enough to a magnet

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**Author:** ![Crusoe](https://avatars.discourse-cdn.com/v4/letter/c/49beb7/32.png) [@Crusoe](https://boards.straightdope.com/u/Crusoe)\
**Post date:** [December 1, 2000, 9:01am UTC](https://boards.straightdope.com/t/credit-cards/43543/3 "2000-12-01T09:01:53Z")

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I’ve had my credit card demagnetised (or whatever the proper term is) by a hotel swipe-card room key before. That was a right pain.

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**Author:** ![Doctor\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doctor_jackson/32/32_2.png) [@Doctor\_Jackson](https://boards.straightdope.com/u/Doctor_Jackson)\
**Post date:** [December 1, 2000, 8:30pm UTC](https://boards.straightdope.com/t/credit-cards/43543/4 "2000-12-01T20:30:42Z")

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To expound a little:  
The black strip you see on the back of a credit card, ATM card, and other “swipe” cards holds various information about you and your account and is encoded magnetically. It’s called, stangely enough, a mag strip or mag stripe. Swipe readers (ATM’s, POS terminals, etc) read the information from the mag strip to validate the card and process the transaction. The reader is looking for data in a particular order and format. Any object which generates a strong enough magnetic field, like some scanners, can interfere with the magnetic field on the card literally rearranging or erasing some or all of the data. When you subsequently swipe the card the data read is garbled or missing causing the reader to reject the card.

Think of your card (at least the stripe) as a floppy disk and the reader as your PC. It works in a very similar manner.

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**Author:** ![Ptrinsey](https://avatars.discourse-cdn.com/v4/letter/p/7ab992/32.png) [@Ptrinsey](https://boards.straightdope.com/u/Ptrinsey)\
**Post date:** [December 4, 2000, 11:51am UTC](https://boards.straightdope.com/t/credit-cards/43543/5 "2000-12-04T11:51:09Z")

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Thanks Doc.

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**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\
**Post date:** [December 4, 2000, 3:23pm UTC](https://boards.straightdope.com/t/credit-cards/43543/6 "2000-12-04T15:23:51Z")

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Yeah, we discussed here how certain wallets can delete info on them too.