A lie-detector “works” if the suspect taking the test believes it works and is intimidated into admitting guilt.
In reality, they are far from accurate.
Which is why the results of a polygraph test is admissible evidence in a criminal trial.
Not admissible evidence. Sorry.
You’re exactly right. Many people fail them because they are intimidated and believe that the test actually indicates a “lie.” But a “lie” is actually whatever physiological indicators the test makers deem to be indicative of not telling the truth, i.e., increase in breathing rate, increase in blood pressure, increased movements as demonstrated through galvanic skin response. This may indicate deception, but more than anything it indicates degree of nervousness, which may have nothing to do with deception.