the.com/lie detector

means A device (typically a polygraph) that records physiological signals like heart rate, blood pressure, breathing, and skin conductivity while someone answers questions, on the theory that lying produces measurable stress.

from The term rides in on 'polygraph,' from Greek 'poly' (many) and 'graphein' (to write) — 'many writings,' because the machine scratches out several body signals on paper at once. The device was developed in the early 20th century, with figures like William Marston (who also, fittingly, created Wonder Woman and her magic lasso of truth) among its popularizers. 'Lie detector' itself is the plain-English marketing name that stuck — vivid and confident, even though the machine detects arousal, not honesty.