CVSA (Computer Voice Stress Analyzer), is basically a lie detector without wires. It uses a microphone plugged into a computer to monitor the subject's reponses. Unlike the polygraph, drugs do not affect the results of the exam.
Micro tremors are tiny frequency modulations in the human voice. When a test subject is lying, the autonomic, or involuntary nervous system causes an inaudible increase in the Micro tremor's frequency. The CVSA detects, measures and displays changes in the voice frequency. The CVSA is not limited to "yes" or "no" answers.
The CVSA was first used during the Vietnam War by U.S. soldiers in an attempt to determine if Vietnamese prisoners were Viet Cong guerrillas or civilians. During that time it was known as the PSE, or Psychological Stress Evalutor. After the war, private developers took over the technology, but it wasn't until the late 1980s that the CVSA became a tool widely used in police investigations.