You exit a busy store, point your key fob across the crowded parking lot, press a button and "Pop!"---your car door unlocks. How does the car know it's you? And why don't other cars open, too?

Most new vehicles offer what the industry calls remote keyless entry. Manufacturers program a microprocessor in each car and in its dedicated key fob with an algorithmic formula that generates a secret, encrypted code that changes each time a button is pressed. Each formula is unique, so one person's fob cannot open any other vehicle. Current-day garage door openers work similarly. "The scheme has been around for 10 years and has proven very secure," says Fanie Duvenhage, product marketing manager at Microchip Technology, a Chandler, Ariz., firm whose code-generating processors run the majority of U.S. automotive fobs.

This article was originally published with the title Open Sesame.

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