A polygraph, commonly known as a lie detector, is a device that measures physiological responses such as heart rate, blood pressure, and respiration while a person answers questions. The underlying theory is that deceptive answers may trigger noticeable changes in these bodily functions, indicating stress or anxiety. During a polygraph examination, a trained examiner asks a series of questions while monitoring the subject's physiological responses. The results are analyzed to determine whether the individual is being truthful or deceptive. However, the accuracy and reliability of polygraphs are subjects of debate within the fields of psychology and law enforcement.