An electrically-powered device intended to be used in a clinical setting to simultaneously measure the concentrations of two or more gases [e.g., hydrogen (H2), methane (CH4), oxygen (O2)] in an exhaled breath sample. It typically uses electrochemical analysis to assist with the diagnosis of various conditions (e.g., breakdown deficiency and/or malabsorption of carbohydrates, lactose intolerance). It is typically a desktop sensor unit with controls and display; a breathing mouthpiece and/or an exhaled-gas sample collector may be included with the device.