1921-lie-detector-3.jpg
Historical Item

Name: Lie Detector or Polygraph Machine


Category: scientific tool

Size/weight: a medium box/light enough for one person to carry with 2 hands

Rarity: Very rare

Value: Fairly expensive

Uses: to detect lying

Description (ca. 1921):

The first decent lie detector was created by John Larson in 1921, he was a University of California student. It began being widely used in 1924 by police departments. The concept behind the test is that lying causes stress, and stress can be measured by breathing, blood pressure, and pulse. A cuff goes around the arm, and sensors go on the body to measure these. The lie detection exam takes around 2 hours. The person adiminstering the test asks a series of control questions so that they can see the readings that they have when not under stress and under stress. The readings of these questions are used to compare against the readings of case-relevant questions. The readings are created by pens that scribble on paper up or down as the persons readings change.

Source:
http://inventors.about.com/od/fstartinventions/a/forensic_2.htm