The CIA, the FBI and other federal agencies are using polygraph machines more than ever to screen applicants and hunt for lawbreakers, even as scientists have become more certain that the equipment is ineffective in accurately detecting when people are lying.

Instead, many experts say, the real utility of the polygraph machine, or "lie detector," is that many of the tens of thousands of people who are subjected to it each year believe that it works -- and thus will frequently admit to things they might not otherwise acknowledge during an interview or interrogation.