Lie detectors (also known as polygraphs) measure vital signs in order to detect when a lie is being told, but by altering vital sign readouts during the control question phase of the test, it is possible to deceive the machine into thinking a lie is the truth. Because a lie detector is easy to fool, and because the process essentially works by tricking the participant initially to gather control data, lie detectors are not recognized as scientifically valid.
Fooling the polygraph
Beating a polygraph test can be achieved in a few fairly simple steps, as follows:
- Invalidating control data
- Answering the main questions
The first part of any polygraph test will be the asking of a series of control questions designed to inadvertently make the subject lie. This gives the operator a control reading that is watched for when the real questions are asked. Lies cause the body to increase heart and breathing rates, while often producing perspiration. In order to invalidate a control question and give a misleading reading, techniques such as hiding a tack in the shoe (and stepping on it once the control questions begin), or thinking of scary thoughts mimic the effects of a lie.
Staying calm, while keeping breathing slow and regular will now make any answer appear as the truth, as the readings will be much smaller than the data gathered during the control phase.