These two principles have now been incorporated into the Truth Machine.

Micro tremors in the voice, which are often not detected by the human ear, produce frequency modulations, which are measured.

The amplitude of the upper and lower sidebands of the frequency spectrum of the voice is also measured.

The results are analysed and shown visually by the columns of LED lights which range from green (low tension) to red (high tension).

The Truth Machine accurately measures changing stress levels in the voice but as each individual's voice reacts differently it is not infallible; the lighting of red LEDs, high stress, is indicative of lying however!