Atoms hold their outer electrons with varying strengths or affinities. By connecting metals with differing affinities with a conductive medium, the metal with less hold on its electrons loses charge to the metal with a greater hold. Depending on the metals used, different voltages are generated. In Hand Battery, the salty dampness of a visitor’s hands when in contact with copper and aluminum plates creates an electrochemical reaction which causes a small current. The small current is registered on a meter. If the visitor places both hands on the same kind of metal connected to either side of the meter, no potential difference is created. The meter has its “zero” in the center of the scale to allow the visitor to change the polarity of the voltage generated by changing to the other type of metal with each hand, (i.e. copper with the left hand and aluminum with the right hand, or aluminum with the left hand and copper with the right hand).