Why Do Magnets Ruin Credit Cards?

The magnetic door lock on your refrigerator is a dangerous spot for credit cards.
i Ryan McVay/Photodisc/Getty Images

When you present your credit card for a payment swipe and it's a no-go, the strip on the back of your card may have fallen victim to a magnet. Exposure to magnets can render your card's electronic data unreadable by some machines. Magnetic dangers for credit cards lurk far and wide -- in stores, hospitals and homes. Both the strength of a magnet and the amount of exposure to the magnetic force affect the strip on the card.

Demagnetization Process

The magnetic strip on a credit card holds important data, such as your name, the issuing bank, the account number, your credit limit and available credit. When a magnet comes in close or direct contact with the card's strip, the magnet smears or rearranges the order of the iron oxide particles that store the data on them, making the card useless for swiping.

Magnets that Can Harm Cards

The magnetic closure on a purse or wallet can corrupt credit card data if the card's strip comes in close -- within 1 inch -- or direct contact with the magnet. A security tag deactivator at a checkout is a danger zone if its deactivation method uses magnets. Don't take your credit cards anywhere near the fridge when you open it. Refrigerators have strong magnets inside their seal that help keep the door shut. If your credit card's magnetic strip gets within 1 inch of the magnets in the door's seal, you risk dinging the data. Magnetic resonance imaging (MRI) machines used in hospitals have strong magnetic fields that can affect the data from a credit card in the purse or wallet of a person in the same room with the machine.

Magnets that Might Harm Cards

Small magnets -- such as the ones people stick to a refrigerator -- probably won't harm your cards unless your card gets cozy with them for an extended period. For example, if you repeatedly rub a small magnet over a credit card's magnetic strip, the magnet might damage the data. Cell phones produce a low magnetic field; however, if you place your credit card against your phone and keep it there, it might result in data downfall.

Things You Can Do to Protect Your Credit Cards

Do not store two credit cards with their magnetic strips pressed together. Over time, this might result in demagnetization. Store your cards in separate slots in your wallet or purse to prevent demagnetization or damage to the magnetic strips. If you don't have credit card slots in your purse or wallet, look for individual plastic or paper credit card holders to protect each card. Never leave your credit cards in a hot car or allow them to tumble around in a purse or bag.

Quick Fixes and Tips

If your credit card won't work, try placing a piece of clear tape over the magnetic strip. A corrupted data strip has background noise that makes it difficult for a card reader to pick up the data, but the tape creates a barrier between the strip and the reader and decreases the background noise, which allows the reader to recognize the data and read the card. If that doesn't work, ask the merchant to enter the card number and expiration date by hand.

It's a myth that eel skin wallets can demagnetize credit cards. If the wallet has a magnetic closure, the magnet could harm the card. However, the eel skin -- electric eel or not -- has no effect on a credit card's magnetic strip, according to the popular rumor-busting website, Snopes.

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