The Bill and Melinda Gates Foundation recently awarded a $498,055 grant to Clemson University to test bracelets that can detect galvanic skin response (GSR) or skin conductance. The goal of the study is to measure the engagement of students in class. Sweat glands are controlled by the sympathetic nervous system so skin conductance can be used a measure of psychological or physiological arousal. The link below describes an Arduino board to IPhone GSR sensor that can be built for benchtop testing.