"Give me Duquesne minus 7, for a nickel."

It was February 1965 on a lonely section of Los Angeles's Sunset Boulevard, and Charles Katz, one of life's little losers, was placing an illegal sports bet over a public telephone. Unbeknownst to Katz, however, the FBI had placed a microphone atop the telephone booth to record this small-time gambler's conversations.

Engineers often mock the law for lagging behind technology. In fact, the law is often far ahead of it. This time it was ahead by nearly 200 years, for after Katz's arrest his lawyers argued that although the framers of the Constitution could not possibly have encountered tape recorders and telephone booths, the Fourth Amendment's ban on "unreasonable" searches nonetheless covered them. Because the FBI had no search warrant, Katz's lawyers said, bugging the phone booth was illegal. In a landmark decision, the Supreme Court agreed, affirming for the first time that electronic surveillance was-constitutionally speaking-a search. "No less than an individual in a business office, in a friend's apartment, or in a taxicab," the majority declared, "a person in a telephone booth may rely upon the protection of the Fourth Amendment."

Equally important was Justice John Harlan's concurring opinion. The government, he argued, could not freely eavesdrop in any place where people have a "reasonable expectation of privacy"-a phrase that even now, four decades later, resonates in the laboratory of Wayne Wolf. An electrical engineer at Princeton University, Wolf leads a research team that is creating a tiny, inexpensive video camera one might glibly describe as a lens glued to a chip. In theory, the camera could be the size of a postage stamp and cost as little as $10, "small and cheap enough to scatter by the dozen," as Wolf puts it. The laws of optics dictate that tiny lenses make low-resolution images, so the researchers are developing software that melds video from multiple cameras located in a single area, producing sharp, real-time images of the entire space. "You could stick them up all over a building and know exactly what was going on inside," Wolf says. "A lot of people would find a use for that."

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MIT Technology Review