The polygraph , as we know it today, was invented in 1921 by John Augustus Larson , a medical student and police officer in Berkeley, California.

When and by whom

  • 1921 : John A. Larson built the first true polygraph, which continuously recorded blood pressure, pulse, and respiration on a rotating drum of smoked paper.
  • He coined the term polygraph (from Greek poly = many, graph = writing) because the device recorded multiple physiological channels at once.

Earlier precursors

Before Larson’s machine, several scientists laid the groundwork:

  • 1878 : Italian physiologist Angelo Mosso used a plethysmograph to detect blood‑pressure changes in response to stimuli.
  • Late 1890s : Italian criminologist Cesare Lombroso adapted a hydrosphygmograph to measure blood‑pressure and pulse in suspects.

These were not full polygraphs , but they showed that physiological changes could be linked to questioning.

Modern polygraph evolution

  • 1920s–1930s : Leonarde Keeler , a student and collaborator of Larson, refined the device, adding ink pens and later galvanic skin response (sweat‑gland activity), creating the prototype of today’s polygraph.
  • Keeler’s Keeler Polygraph became the first widely used, mass‑produced lie‑detector machine in law‑enforcement work.

Quick summary table

Milestone| Year| Key figure(s)| What changed?
---|---|---|---
First true polygraph| 1921| John A. Larson| Continuous recording of BP, pulse, and respiration. 13
Early blood‑pressure measurements| 1878–1890s| Mosso, Lombroso| Used single‑channel instruments to track BP/pulse under stress. 1
Modern ink‑based polygraph| 1925–1938| Leonarde Keeler| Added ink pens and galvanic skin response; first mass‑produced model. 524

Information gathered from public forums or data available on the internet and portrayed here.