The hardware consists of nothing more than an Arduino, a 10K resistor, wire and some tin foil. (You didn’t use ALL your foil for your hat, did you?) The device operates on the galvanic skin response (GSR) principle and detects changes therein via a foil band around your finger. The ends of the band are connected between the two open leads as depicted in the above diagram, with the Arduino taking readings on Analog pin 0. Readings are displayed on your PC as a graph using Processing.
All source code (both Arduino and Processing sketches) is contained in the Arduino Communications/Graph example within the Arduino IDE.