Credit card Magnetic strip and the plastic bag trick

[Rolliet]

When my credit card magnetic strip is worn it won't scan at the grocery check out. The clerk then uses a plastic bag over the card and runs it through the scanner. I'm baffled why this should work, but it does every time. Any explanations ?
Thanks

 

[ModusPwnd]

This is a fault of your card rather than their scanner?

 

[DrZoidberg]

If you had googled your question, you would have found this site
http://blogs.howstuffworks.com/2009...magnetic-stripe-on-the-back-of-a-credit-card/

 

[Rolliet]

Yes, a problem when a card gets old. I'd think it happens to everyone.

 

[sophiecentaur]

The separation by the bag must be, effectively, a low pass filter - reducing noise and 'sidebands', due to the scratches (modulation of the basic stripe frequencies). It can't be more than that. I don't know why the scanner couldn't do this for itself, in a more efficient and adaptive way. Maybe the newer generation scanners work better. It would need a 2D array of sensors to do best.

 

[256bits]

... I don't know why the scanner couldn't do this for itself, in a more efficient and adaptive way. ...

I think you would still come to the same situation, but with a card more scratched up, after a time.

 

[sophiecentaur]

Hopefully, the card would be out of date by that time.