When a water drop contacts with narrow wires composed of different metals with a small gap “like a bridge”, electrical voltage and current are generated by the galvanic action, which is a type of the electrochemical ones. This working principle can detect fine water derived from environment such as moisture. It’s not possible by conventional technologies such as commercial hygrometer. Our group is aiming for realization of small sensor which can detect fine water with a high sensitivity, accuracy and quick response.