Magnetic Strips and How They Work

Magnetic strips, which grace everything from credit cards to airplane tickets, are direct descendants of the magnetic tape lurking inside a music cassette. The strip is a thin layer of plastic mixed with a powder that's made of some material strongly attracted to magnets. Often, it's a relative of iron oxide (that's rust, to me and you). Using a device that generates a strong magnetic field -- a.k.a., a read-write head -- different magnetic bits in the strip can be magnetized in different directions, in a kind of code that's readable to any machine with the right equipment.

Since a moving magnetic field encoded the card, moving the card across the proper read head can generate tiny voltages that the reader can amplify and pass on to a computer. This data can include everything from your name, rank and serial number to what you had for breakfast last Tuesday (if your company really wants to go that far). If the computer like what it sees, you're in. If not, you're left standing out in the cold.

There are certain things you never want to do if you want to be able to get inside your office the next day. Don't scratch or rub off part of the strip. Don't come too near a strong magnet -- even a fridge magnet can be murder on a mag strip badge. And whatever you do, don't leave it baking in the sun on the dashboard of your car. Even if the radiation from the sun doesn't damage the information on the strip, the plastic might deform or melt enough to make the card unreadable.

On to part eight :: Biometric Badges :: Back to Index