The prevailing scientific opinion on lie detector tests is that they don't work well enough to be relied on in courts as evidence - in fact, they're probably not even a good way of discerning the truth. Unfortunately a Christchurch based private detective is selling tests to couples (opens new window) as a way of finding out whether a partner has cheated.

Lie detector tests measure biometric indicators, and this particular test (the Lafayette LX5000) measures breathing, heart rate, blood pressure and finger sweating. Barry Newman claims a 96% accuracy for his testing, a value he seems to base on a cherry picked study.