How accurate are lie detector tests?

The accuracy of lie detector (polygraph) tests varies significantly depending on multiple factors. Results can differ based on the person administering the test, the machine used, and especially the individual being tested. Due to this wide variability in accuracy, most states don't allow polygraph results as evidence in criminal court unless both parties agree to it. Even with agreement, many states still prohibit the admission of polygraph results as evidence in criminal cases, recognizing their unreliability despite how TV shows might portray them as 100% accurate.