Voice stress tests are the new polygraph. The technology records a suspect's voice when he answers easy questions ("What's your name?) and hard questions ("Did you do it?").
It then compares the two, looking for voice pattern changes that are thought to be indicative of psychological stress or lying.
Over 1,800 law enforcement agencies nationwide use at least some form of the technology. But are voice stress tests even admissible at trial?
They may not be -- but it ultimately depends on the specific court.
When deciding whether to admit expert scientific testimony, federal judges must consider whether:
- It is based on a theory or technique that can be and has been tested;
- Those tests were subject to peer review;
- The technique has a high known or potential rate of error; and
- The theory is generally accepted within the scientific community.
State rules may differ, but most of them are based on federal law. At the very least, they tend to require that the technology or theory be generally accepted as sound.
It is this requirement that would likely prevent voice stress tests from being admissible. Experts are split as to whether the technology is reliable. In a strongly worded study published by Justice Department's National Institute of Justice, voice stress tests are said to be "no better than flipping a coin when it comes to detecting deception."
Polygraph tests receive similarly mixed reviews, and have themselves been prohibited by many courts. Some federal judges allow them into evidence, but many states have prohibited their use unless both parties agree to their admission. If the polygraph is any indication, few judges will find voice stress tests admissible at trial.