One problem: lie detectors do not detect lies.
This is one of the prevaling myths in our country. Take it away APA
Lie detector tests have become a popular cultural icon - from crime dramas to comedies to advertisements - the picture of a polygraph pen wildly gyrating on a moving chart is readily recognized symbol. But, as psychologist Leonard Saxe, PhD, (1991) has argued, the idea that we can detect a person's veracity by monitoring psychophysiological changes is more myth than reality. Even the term "lie detector," used to refer to polygraph testing, is a misnomer. So-called "lie detection" involves inferring deception through analysis of physiological responses to a structured, but unstandardized, series of questions.The lie detector is less obvious fantasy than another iconic creation of early polygraph enthusiast William Moulton Marston: the Wonder Woman and her lasso of truth.
This persistent popular myth about lie detectors also has dangerous implications for national security. After all, Aldrich Ames passed his lie detector test.
For more on the history of the lie detector and America's fixation on it, see Ken Adler's The Lie Detectors: The History of an American Obsession. Or perhaps more convenient than having to read an entire book, see the entry on polygraphs at the Skeptic's Dictionary.