Overview:

This simple lie detector that can be built in a few minutes, but can be incredibly useful when you want to know if someone is really telling you the truth. It works by measuring skin resistance, which goes down when you lie.  

Schematic

Parts List

 

Part	Description	Quantity
R1	33K 1/4W Resistor	1
R2	5K Pot	1
R3	1.5K 1/4W Resistor	1
C1	1uF 16V Electrolytic Capacitor	1
Q1	2N3565 NPN Transistor	1
M1	0-1 mA Analog Meter	1
MISC	Case, Wire, Electrodes (See Nots)	1

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.

This is not 100% accurate with all people but still makes for a fun project.