Why Does Wrapping a Credit Card in a Plastic Bag Help It Swipe Successfully?

[becz-]

I have a credit card that I use quite more often then others, and obviously the magnetic strip on the back of the card has worn down quite a bit. Often, when someone slides the card it doesn't read properly and the cashier person has to manual type in my card number. Someone told me if you put the credit card in a plastic bag, such as a shopping bag from Walmart, and slide the card while its in the bag, it will read. Now when my card doesn't read, I tell the cashier to put in it in a plastic bag and it always works. What about the card being in a plastic bag makes the magnetic strip work? Thanks in advanced for any replies, my Physics professor couldn't figure it out.

 

[Tide]

I think the problem is that scratches on the surface of the magnetic strip produce spikes in the reader which causes the checksum to fail. Placing a plastic bag over the card (strip) prevents those spurious readings.

 

[Danger]

Applying cellophane (Scotch, etc.) tape to the stripe can be effective as well, and a bit handier.

 

[pallidin]

I would opt to GET A NEW CARD. It's simple, free and takes about a week or 2. As a side note, men are more prone to damaging credit cards than women due to where men generally keep them... in their wallet behind their butt, which can crack and damage a card.
Other solutions might remedy an emergency condition, but, GET REAL. You need a new card. ITS FREE.

Sometimes I will use http://www.creditcounselorhut.com if I want some paid advice.

 

[becz-]

I would opt to GET A NEW CARD. It's simple, free and takes about a week or 2. As a side note, men are more prone to damaging credit cards than women due to where men generally keep them... in their wallet behind their butt, which can crack and damage a card.
Other solutions might remedy an emergency condition, but, GET REAL. You need a new card. ITS FREE.

K well, the question wasn't whether or not I needed a new card. I'm fully aware it's free and easily ordered and a task that can be done over the phone in 3 minutes. I was asking about the reasoning behind it working with the plastic bag. Thanks for your side note.

 

[becz-]

for anyone who was truly interested in the answer.. i found it on http://www.straightdope.com/columns/040116.html


Dear Cecil:

I've heard of this before, but didn't believe it. Now I've seen it for myself, and my
skeptical mind needs a good explanation. A lady in front of me at the supermarket swiped
her credit card but it didn't work. She tried again, didn't work. The cashier tried,
didn't work. So far, everything was proceeding scientifically. Then the cashier says, "My
friend who works at a bank taught me this." What's he do? He puts the credit card in a
plastic shopping bag, pulls the plastic tight around the card, and swipes it. Now the
part I don't get: It worked. --Tim, Newton, Massachusetts

Cecil replies:

At least the cashier's friend didn't tell him to bury the card at a crossroads at
midnight. Wacky though the plastic-bag technique seems, several of Cecil's engineering
buddies admit they've seen it work. Here's the deal. Standard bank cards use the F2F
(Aiken biphase) modulation scheme, in which flux reversals encoded in the . . . eh, too
much information. Let's just say that when you swipe the card through the reader, the
magnetized particles in its stripe generate a signal with "ticks" in it at intervals that
the machine is able to interpret as digital ones or zeros. A scratch or other defect in
the magnetic stripe can cause a spike (i.e., brief fluctuation) in the signal that a
too-sensitive reader will interpret as a tick, meaning that the encoded data will fail
the parity check (the numbers won't add up right) and the card won't work. Wrapping the
card in plastic increases the distance between the read head and the magnetic stripe,
thus reducing the strength and crispness of the signal and smoothing out anomalous
fluctuations. Behold, the card works. Worth a try, anyway--God forbid the clerk should
have to punch in the numbers by hand.

--CECIL ADAMS