A false positive can occur when someone telling the truth triggers the device, which then may indicate he’s lying even if he isn't. Because of this, polygraph results aren’t admissible evidence in any state. Some states prohibit them entirely, while others will admit the results if all parties to the lawsuit or trial agree.

In most instances, failing a polygraph test warrants a retake to verify the initial result. Someone who gets a false positive result, which means that a truthful person is reported as deceitful, usually passes the exam the second time around. Either way, a lie detector test result is not admissible in most courts.