On 13 January 1931, US Patent No. 1,788,434 was granted to Leonarde Keeler for an “Apparatus for recording arterial blood pressure”.
Keeler’s device, known as the Emotograph, turned physiological reactions into a readable trace, using instrumentation and a chart recorder to capture changes that would otherwise vanish in the moment.
This patent marks an early step on the road to the modern polygraph. It reflects how lie detection technology evolved through practical engineering, better recording methods, and the drive to standardise what had been improvised experiments.
Leonarde Keeler
Drawings from US Patent No. 1,788,434 for an “Apparatus for recording arterial blood pressure”.
| Country | Kind | No. | Published | Title | Download |
|---|---|---|---|---|---|
| US | Patent | 1,788,434 | 13.01.1931 | Apparatus for recording arterial blood pressure |
Last updated on 18 February 2026