sysadmin field notes : ATM Cards

ATM Cards

June 16, 2005

Ever had a card intermittently fail to read? My ATM card (that was thankfully just replaced) would read someplaces and not others. Or it would take 2-3 attempts to get it; this went on for about a year. The card had obviously become partially demangetized.

During this time it was subjected to an amazing amount of home grown techniques by store clerks to get it to read. These include:

Putting cellophane tape over the strip (without asking)
Rubbing hand lotion on the strip
Putting the card in a plastic bag and swiping it
Trying to remove the cellophane tape
Rubbing quickly on jeans

I don't know what my favorite is. I wish everyone would just leave my card alone. Try it 3-4 times at different speeds and directions, and if it doesn't read, please don't abuse it any further. Number 5 seems like the easiest to dream up a half-explanation for; static electricity generating some extra coercivity or something maybe. It's certainly better than the tape or the hand lotion.

I think all of this is observational bias and incorrect reinenforcement. Since broken cards are often intermittent, if you run them 4-5 times you'll probably get one to work. If that happens 2-3 times after applying hand lotion, then hand lotion just became the ATM card cure-all, no matter how many times it fails to work.

Anyone else have strange things done to their magnetic stripe cards?

Posted by rmeyer at 8:56 AM

Comments

Posted by fb3 at June 20, 2005 2:54 PM

Ah, yes, the plastic bag trick. Until my old card finally gave up the dust, I actually sought out new places to find out what they would try on it. In my experience, the plastic bag trick was the crowd favorite.

Posted by neil at June 25, 2005 12:54 AM

I'm pretty sure that all atm and credit cards are encoded palindromically. In other words, the magnetic strip reads "|".

You might consider just swiping it backwards.

Posted by neil at June 25, 2005 12:55 AM

s/"|"/"real data|atad laer"/

stupid blog software.

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Sysadmin Field Notes

ATM Cards

June 16, 2005