How the Lie Detector (Polygraph) Works?

 

When a person takes a polygraph test, four to six sensors are attached to him. A polygraph is a machine in which the multiple ("poly") signals from the sensors are recorded on a single strip of moving paper/Computer ("graph").

 

The sensors usually record:

• The person's breathing rate

• The person's pulse

• The person's blood pressure

• The person's perspiration

 

When the polygraph test starts, the questioner asks three or four simple questions to establish the norms for the person's signals. Then the real questions being tested by the polygraph are asked.

 

Throughout questioning, all of the person's signals are recorded on the moving paper.

Both during and after the test, a polygraph examiner can look at the graphs and can see whether the vital signs changed significantly on any of the questions.

 

In general, a significant change (such as a faster heart rate, higher blood pressure, increased perspiration) indicates that the person is lying.

 

Our Polygraph machine is fully computerised and is able to measure in minutes changes in these vital signs.