why do magnets erase credit cards after an update?

The Deep Dive

Credit cards store data on a magnetic stripe, a thin film composed of tiny iron-based magnetic particles. Each particle acts like a miniature magnet, and its orientation (north-south polarity) is precisely set to represent binary data (0s and 1s). When a credit card is "swiped," a read head detects these magnetic orientations, translating them back into account information. Magnets work by creating a magnetic field. If a strong enough external magnetic field comes into contact with the stripe, it can reorient these microscopic magnetic particles randomly or uniformly in a way that doesn't correspond to the original data. This process, known as demagnetization, scrambles the stored information, making it unreadable by card terminals. The strength required to demagnetize a stripe depends on its "coercivity" – a measure of its resistance to demagnetization. Older cards often used low-coercivity (LoCo) stripes, making them more vulnerable, while newer cards generally feature high-coercivity (HiCo) stripes that are more resistant but not entirely immune to very strong magnetic fields. The idea of an "update" causing this is a misunderstanding; the magnetic field directly corrupts the physical data on the stripe, independent of any software or system updates.

Why It Matters

Understanding how magnetic stripes work and their vulnerability highlights critical aspects of data security and convenience. The susceptibility of magnetic stripes to demagnetization led to the widespread adoption of EMV (Europay, MasterCard, and Visa) chip cards. Chip cards store data securely within an integrated circuit, making them far more resistant to magnetic interference and more difficult to counterfeit. This transition significantly enhances transaction security, reducing fraud and ensuring reliable access to funds. Knowing this also encourages responsible handling of cards, keeping them away from strong magnets found in wallets, phone cases, or electronic devices, even though chip cards are now prevalent.

Common Misconceptions

A common misconception is that all magnets will instantly erase a credit card, or that only "updated" cards are vulnerable. In reality, the strength of the magnetic field and the card's coercivity determine the risk. Weak magnets, like those often found in refrigerator magnets or older phone cases, might not be strong enough to affect a high-coercivity stripe. Another myth is that EMV chip cards are equally susceptible. Chip cards store data digitally on a microchip, not a magnetic stripe, making them virtually immune to magnetic demagnetization. While they still have a magnetic stripe for backward compatibility, the primary, more secure transaction method uses the chip.

Fun Facts

• The first magnetic stripe cards were developed in the 1960s by IBM for the US government, initially for employee identification.
• High-coercivity (HiCo) magnetic stripes, typically black, are more resistant to demagnetization than low-coercivity (LoCo) stripes, which are usually brown.