After watching big bang theory last night on iplayer I was inspired by the piece on lying. This is something we all do and evidently learn from a young age.
Turns out one of the main physiological measures used by the polygraph Galvanic Skin Response or GSR (medics preffer Electrodermal Response or EDR). In simple terms the resistance of the body changes based on the sweat gland activity which is in turn a good indicator of stress or arousal [lego mindostorm project]. If you link this with other physiological measures such as heart rate and possibly respiration you can get a picture of when a lie is being told. Turns out a the sensor to measure GSR consists of two dry electrodes. A heart rate monitor is a bit more sophisticated (= expensive) and breathing could probably be done with a stretch sensor.
Conducting some experiments and observing values changing will allow a model or collection of thresholds which may signify a lie. (in practice I suspect it may also respond to printer rage, taking the stairs, and that fourth espresso you don't need but have anyway)
Having gained some experience of the wifi shield offered by async labs it would not be a huge jump to produce a wifi enabled wearable device that tweets when you are lying! or at least rates how aruosed you when you share with your followers that it was corflakes to day not shreddies vs just chiansawed by leg off.
