A magnetic strip (often called a magnetic stripe or “magstripe”) is the thin, dark band on the back of credit cards, debit cards, hotel key cards, and ID badges that stores data using tiny magnetized particles. When you swipe a card through a reader, the stripe transmits information like your account number to complete a transaction or grant access. Though the technology dates back to the 1960s and is gradually being replaced by chip and contactless payments, magnetic stripes remain on billions of cards worldwide.
How a Magnetic Strip Stores Data
The stripe itself is a layer of tiny iron-based particles embedded in a plastic resin, bonded to the surface of a card. Each of those particles is a miniature magnet with a north pole and a south pole. Data is written to the stripe by running it past an electromagnetic write head that flips the polarity of these particles in specific patterns.
The key concept is the “flux reversal.” When two neighboring particles face the same direction (north-to-north or south-to-south), their magnetic fields repel each other, creating a detectable spike in magnetic energy at the boundary. A series of these flux reversals along the length of the stripe encodes binary data: patterns of 1s and 0s that represent your account number, expiration date, and other card details. The stripe on a standard payment card has three separate tracks, each carrying different pieces of information at different densities.
What Happens When You Swipe
Swiping a card through a reader is a straightforward application of electromagnetic induction. Inside the reader is a small pickup coil. As the magnetized stripe slides past that coil, the rapidly changing magnetic fields along the stripe create tiny voltage pulses in the coil. Each pulse corresponds to a flux reversal on the stripe, and the reader translates that sequence of pulses back into the original data. The faster you swipe, the stronger the voltage signal, which is why swiping too slowly can cause a read error.
HiCo vs. LoCo Cards
Not all magnetic stripes are created equal. The two main types differ in coercivity, which is how strongly the particles resist being remagnetized.
- HiCo (High Coercivity): Encoded at around 2,750 Oersted, these stripes are typically black. Because they require a stronger magnetic field to write or erase, they’re more durable and harder to accidentally demagnetize. Credit cards, bank cards, library cards, and employee ID badges use HiCo stripes.
- LoCo (Low Coercivity): Encoded at roughly 300 Oersted, these stripes are usually brown. They’re cheaper to produce but far easier to erase, making them suited for short-term use. Hotel room keys, theme park passes, and gift cards typically use LoCo technology.
This difference explains a common frustration: your credit card survives years in your wallet near a phone case magnet, but your hotel key card stops working after a day in the same pocket. A typical HiCo credit card needs exposure to about 4,000 gauss to demagnetize, while a LoCo hotel key can be wiped by a field of just 300 gauss or less. Purse clasps, phone case magnets, and even the magnetic closures on tablet covers can generate enough force to blank a LoCo card.
Where the Technology Came From
IBM engineer Forrest Parry invented the magnetic stripe card in the early 1960s while trying to create a more secure identity card for CIA officials. His challenge was bonding a piece of magnetized tape to a plastic card. According to IBM’s own account, the approach Parry developed was standardized as a US standard in 1969 and adopted internationally two years later, allowing magstripe cards to be used anywhere in the world. That universal compatibility turned the magnetic stripe into the backbone of global payment systems for decades.
Why Magnetic Strips Are a Security Weakness
The fundamental problem with magnetic stripes is that they store static data. Every time you swipe your card, it transmits the exact same account information. A criminal who captures that data, even once, can write it onto a blank card and use the clone for fraudulent purchases. This is exactly what card skimmers do: small devices placed over legitimate card readers at ATMs or gas pumps that secretly record the stripe data as you swipe.
Chip cards (EMV cards) solve this by generating a unique, one-time code for every transaction. Even if someone intercepts the data from a single chip transaction, it’s useless for making another purchase. This is the core reason the industry has been pushing to retire the magnetic stripe.
The Phase-Out Timeline
Mastercard has published a specific roadmap for eliminating magnetic stripes from its cards. Starting in 2024, newly issued Mastercard credit and debit cards are no longer required to have a stripe in regions like Europe where chip readers are already universal. U.S. banks will no longer be required to include a magnetic stripe on new chip cards starting in 2027. By 2029, no new Mastercard cards will be issued with a stripe at all, and by 2033, magnetic stripes will be completely gone from all Mastercard credit and debit cards in circulation. Prepaid cards in the U.S. and Canada are currently exempt from this schedule.
Other major card networks are following similar timelines, though the exact dates vary. The transition is deliberately gradual because millions of merchants, particularly in developing markets, still rely on swipe-only terminals. The stripe won’t vanish overnight, but for most cardholders in North America and Europe, the swipe is already a backup method rather than the default.