The father of the modern lie detector was Dr. William Marston, a Harvard psychologist perhaps better known for creating the comic-book character Wonder Woman under the nom de plume "Charles Moulton."

Marston's contribution to the science of the detection of deception is more method than instrumentation. He believed that verbal deception could be detected by changes in the systolic blood pressure. He used a standard a blood pressure cuff, or sphygmomanometer, to take measurements of systolic blood pressure during interrogation.  

This was the first time anyone used any kind of an instrument to detect truthfulness or deception. His method was simple. Take and record the subject's blood pressure, release the cuff. Ask the subject a question. Take and record the subject's blood pressure once again to identify any changes. He called this the "discontinuous method" of detecting deception.

Later in his work with lie detection, he used a pneumograph to record respiration cycles. But, both the sphygmomanometer and the pneumograph were separate instruments.

William Marston was involved in a landmark criminal case, Frye v U.S., in 1922 that established the current legal precedent on the admissibility of scientific evidence. Many myths abound about this case. Jim Fisher has written an article about this case that finally sets the record straight. It can be found at:

          http://jimfisher.edinboro.edu/forensics/frye.html