who invented the lie detector

The lie detector, also known as the polygraph, was invented by John Augustus Larson in 1921. Larson was a medical student who developed the first device capable of measuring multiple physiological indicators—blood pressure, pulse rate, and breathing rate—simultaneously during questioning to detect deception. He presented this invention to aid criminal investigations with the Berkeley Police Department. Later, Leonard Keeler improved the polygraph by adding features like recording ink pens and the measurement of skin electrical resistance, creating a device similar to modern versions. Before Larson's invention, important foundational work was done by others, including William Moulton Marston, who invented an early version of the lie detector focusing on systolic blood pressure, and Italian researchers like Angelo Mosso and Cesare Lombroso, who studied physiological changes related to lying. However, Larson is considered the "father of the polygraph," while Keeler is known as the "father of the modern polygraph".