SUBBITT

I built it for myself and as a requirement of a "self creation" while attending Brown Institute where I got my degree at. It was called a "Vocal Stress analyzer" which I found the schematic and plans for in a magazine like Radio Electronics - Years Ago!. Thanks to google I have found a device very similar in operation offered in a build it yourself "Kit" form:

(It worked about as well as reported in this video on it at msnbc :) )

http://www.vectronics.com/man/pdf/VEC-8210K.pdf

General Information: According to an old saying, "truth takes many forms".
Based on recent research, one form it may take is vocal relaxation. Studies
show that when humans speak truthfully, the nervous system relaxes its grip on
the larynx--allowing muscle pairs to "wander" slightly during the articulation of
words. This, in turn, produces a tell-tale low-frequency tremolo that may be
monitored electronically. Conversely, when humans step onto the slippery slope
of prevarication, the nervous system involuntarily tightens its grip--possibly to
ensure the deception will "sound right" when it comes out! When this happens,
low-frequency vocal modulation diminishes.
Even specially trained interviewers and speech therapists can rarely detect such
subtle changes in speech with "the naked ear". However, with the help of your
VEC-8210K BS Meter, you can watch the change occur on a graphic LED
display. Of course, results generated by your kit should be read with caution and
never offered for any official purpose. Certified voice-stress analysis normally
utilize highly sophisticated bio-medical instrumentation, and the results are
subject to skilled interpretation.
Circuitry: Your VEC-8210 uses the log-amp function built into the NE-614
FM-receiver IC to compress speech signals--much like the limiter stage of an
FM receiver. A quad op-amp then filters and level-detects the low-frequency
"tremolo" sideband produced by the compressed signal, and sends a dc output
level to a LED display driver and 10-segment LED metering display. When the
larynx is relaxed, BS Meter readings flicker up and down much like a Vu meter.
But, when a veil of deceit masks the truth, those flickerings become eerily
subdued