Simple Lie Detector

Parts
R1             33k
R2             5k pot
R3             1.5k
C1             1uF   16v electrolytic capacitor
Q1             2N3565 NPN transistor
M1             0-1mA analog meter
mics            wire,electrodes

Notes

1. The electrodes can be alligator clips (although they can be painful), electrode pads (like the type they use in the hospital), or just wires and tape.
2. To use the circuit, attach the electrodes to the back of the subjects hand, about 1 inch apart. Then, adjust the meter for a reading of 0. Ask the questions. You know the subject is lying when the meter changes.

source