A lie detector is an electronic machine used mainly by the police to find out whether a suspect is telling the truth.
...the results of a lie detector test.
lie detector in British English
noun
a polygraph used esp by a police interrogator to detect false or devious answers to questions, a sudden change in one or more involuntary physiological responses being considered a manifestation of guilt, fear, etc
polygraph (sense 1), galvanic skin response
lie detector in American English
US
a polygraph used on persons suspected of lying: it records certain bodily changes assumed to occur when the subject lies in answering questions
Examples of 'lie detector' in a sentence
lie detector
It will be the middle classes who are connected up to the lie detector and asked about their tax affairs.
Times, Sunday Times (2010)
Two couples take a lie detector test... will their love survive the results?
The Sun (2008)
The accusation was driving the family apart, but the father preferred the lie detector to the police.
Times, Sunday Times (2012)
I've asked my girlfriend to take a lie detector test but she refused.