Bersin, a self-assured bureaucrat and a Rhodes Scholar who studied at Oxford with Bill Clinton, approaches the device. The lower monitor displays an icon of an oversize red button; the upper screen shows the head and shoulders of a smoothly rendered, computer-generated young man blinking and occasionally suffering a slight electronic shudder. He appears to be in his twenties and has an improbably luxuriant head of blue-black hair combed back in a sumptuous pompadour. This is the Embodied Avatar, the personification of the latest software developed to help secure the nation’s frontiers by delivering what its creator calls “a noninvasive credibility assessment”—sifting dishonest travelers from honest ones. Which is to say, this late-model Max Headroom is a lie detector.

Since September 11, 2001, federal agencies have spent millions of dollars on research designed to detect deceptive behavior in travelers passing through US airports and border crossings in the hope of catching terrorists. Security personnel have been trained—and technology has been devised—to identify, as an air transport trade association representative once put it, “bad people and not just bad objects.” Yet for all this investment and the decades of research that preceded it, researchers continue to struggle with a profound scientific question: How can you tell if someone is lying?

That problem is so complex that no one, including the engineers and psychologists developing machines to do it, can be certain if any technology will work. “It fits with our notion of justice, somehow, that liars can’t really get away with it,” says Maria Hartwig, a social psychologist at John Jay College of Criminal Justice who cowrote a recent report on deceit detection at airports and border crossings. The problem is, as Hartwig explains it, that all the science says people are really good at lying, and it’s incredibly hard to tell when we’re doing it.

More: Deception Is Futile When Big Brother’s Lie Detector Turns Its Eyes on You