Had the ancient Greeks tried to use their Trojan horse to sneak into the Department of Energy's Y-12 facility in Oak Ridge, Tenn., they would almost certainly have given themselves away by a sound they couldn't control: the beating of their own hearts. Engineers at the national laboratory have developed a technology so sensitive it can pick up the sound of a heartbeat even when a person is well hidden inside a large vehicle.

The aim of the heartbeat detector is to catch terrorists attempting to gain entry to secured sites, prisoners trying to escape from jail, illegal immigrants crossing borders, even endangered animals being smuggled into the United States. So successful are early versions of the technology that it is being tested in maximum security prisons in California and in Tennessee.