Possible causes of a defective card:

Mobile phone
The loudspeaker magnets used in all mobile phones create a static magnetic field, which can demagnetise the card’s magnetic stripe. More precisely, it can erase the encoding, rendering the card unusable.

Magnetic pocketbook clasps
Watch out ladies! Magnetic pocketbook clasps can also erase the data contained in magnetic stripes, though this usually only happens if the card comes in direct or very close contact to the pocketbook’s magnetic clasp.

Mobile phone belt pouch
Belt pouches for mobile phones, Blackberries or cameras are becoming increasingly popular. Most of them feature a magnetic clasp and some are even equipped with pockets to hold cards. This is a dangerous combination: The clasp’s magnetic field can permanently damage the card’s magnetic stripe.

Merchandise theft protection systems
Theft protection systems for merchandise commonly used to “disarm” articles at the cashier in many shops can damage a card’s magnetic stripe; especially if the card is placed on the counter right next to the disarming system. Many stores are beginning to call attention to this risk by posting warning stickers and information in the cash-till area.

Loudspeakers, televisions
Depending on a loudspeaker or television’s magnetic shielding, a card’s existing data can be erased when placed on top of one of these devices.

Magnetic keys
If a magnetic key comes into contact with a card’s magnetic stripe, the key’s magnetic field may erase the card’s data. It is always best to keep cards and keys apart.  

Paperclip holders
They may be very practical, but they are hazardous to cards: Paperclip holders often use a magnet to prevent the paperclips from spilling out. While the emitted magnetic field is not very strong, it is enough to damage a card’s magnetic stripe if the card is placed too close to the paperclip holder.

X-rays, magnetic resonance tomography (MRT)
X-rays and, in particular, magnetic resonance tomography also pose a threat of erasing data content from magnetic stripes. This is especially true at the dentist: Dental x-rays are usually taken while the patient is fully clothed, rendering magnetic stripe cards illegible and, thus, unusable. Always put magnetic stripe cards in a safe location prior to a dental examination.

Magnetic ski racks
They may only be used in the winter, but magnetic ski racks can destroy magnetic stripes: The powerful magnets they use can erase card data immediately, so extreme caution is advised. By the way, data contained in ski passes can also be erased this way.   

Here are a few other tips on how to keep magnetic stripe cards functioning for as long as possible:

• Cards tend to warp when exposed to temperatures above 60° Celsius, which can be easily exceeded inside parked vehicles on a hot summer day. Therefore, cards should not be left in the car.
• Cards should not be carried together with loose change, because coins can damage cards.
• Avoid carrying cards in a back pocket where they can be easily bent.
• Always try to keep cards in a protective case.

And by the way: Both the chip and magnetic stripe must be intact to complete a valid transaction, so be sure they are both in working order. If a chip malfunctions, try to remedy it the same way you would a magnetic stripe: By wiping it on a clean piece of clothing.

Finally, it should be mentioned that an error message can sometimes be traced back to the card terminal or to temporary system unavailability. Therefore, it is not necessary to order a new card by the first failed attempt.