THE US Department of Defense (DoD) has revealed plans to develop a lie detector that can be used without the subject knowing they are being assessed. The Remote Personnel Assessment (RPA) device will also be used to pinpoint fighters hiding in a combat zone, or even to spot signs of stress that might mark someone out as a terrorist or suicide bomber.

In a call for proposals on a DoD website, contractors are being given until 13 January to suggest ways to develop the RPA, which will use microwave or laser beams reflected off a subject's skin to assess various physiological parameters without the need for wires or skin contacts. The device will train a beam on "moving and non-cooperative subjects," the DoD proposal says, and use the reflected signal to calculate their pulse, respiration rate and changes in electrical conductance, known as the "galvanic skin response." "Active combatants will in general have heart, respiratory and galvanic skin responses that are outside the norm," the website says.

Because these parameters are the same as those assessed by a polygraph lie detector, the DoD claims the RPA will also indicate the subject's psychological state: if they are agitated or stressed because they are lying, for example. So it will be used as a "remote or concealed lie detector during prisoner interrogation".

But finding ways to fulfil the DoD's brief will pose a practical challenge, says Robert Prance, an electrical engineer at the University of Sussex , UK , who specializes in non-invasive sensors. "They might capture breathing rate with an infrared laser that senses chest vibration, but how they will measure a pulse through clothes, for instance, is a very big question."


If the RPA is ever produced, it is likely to prove controversial. A remote lie detector would face even more difficulties than standard polygraph tests, which were themselves the subject of a damning 2003 report from the US National Academy of Sciences. "There is no way a polygraph test can be carried out usefully without the subject knowing, because you actually want the person to worry about certain questions," says Bruce Burgess, an examiner with polygraph firm Distress Services of Leatherhead, Surrey, UK.

But Steve Wright, a conflict analyst at Leeds Metropolitan University , UK , raises the prospect of people identified as suspects by the device being captured and subjected to secret "prisoner rendition" as a result. And he warns that the RPA could introduce a "chill factor" into everyday life.

From issue 2533 of New Scientist magazine, 05 January 2006 , page 22