It's pretty amazing technology — and all on such a small scale. I learned that our shiny new ID badges are encoded with around 100 bytes of information, all neatly packaged on those little black strips on the back, called "magstripes." And there are universal rules that everyone — from Visa and MasterCard right down to the customer loyalty cards at the local CVS — has to follow. All the cards have the exact same size magstripe, in the exact same position, and every stripe encodes three tracks of information. It just depends on how and why you use what that strip holds. The magnetic card readers on the doors of our building read the info that's contained on the magstripe when we swipe our badges, and then one of two things happens: the door opens to let you in, or the alarm starts going off and the cops are at the door in a matter of minutes.