TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: Concentration of CO detected by the sensor(s) is displayed on a display device. Temperature of HRS is reduced before it is routed to the chambers.The chambers comprise sensor(s) optically responsive to CO at increasing threshold and decreasing sensitivity, a photon source (261, 261a) for emitting photons on to the sensor and a photodetector (262, 262a) for receiving photons emitted on the sensor.An alarm signal is provided when the concentration of CO exceeds a predetermined set point.A differential measurement from a control sensor and a catalytic sensor is used to determine concentration of CO in HRS.The control sensor and the catalytic sensor are equally responsive in an air environment in the absence of CO.Concentration of CO is determined using a microcomputer to some entries of the table of differences, to add the summated series in an alarm register and enter alarm mode or control mode when the alarm registers exceed preset activation point.A control sensor, circuit and an optical comparison equipment are used to measure difference between the sensors in the chambers and the control sensor.The apparatus has an equipment for providing an output signal when the concentration of CO reaches a predetermined set point.Valve(s) (254a) in the HRS control passage of the stream to the chambers.The fresh air stream has valve(s) (254) to control the passage of air into the chambers.The apparatus has an equipment between a reformer and the fuel cell to reduce the concentration of the target gas in the HRS when above a preset amount.The apparatus for reducing the concentration of CO has a metal catalyst which converts the target gas to a hydrocarbon fuel.The equipment for reducing the concentration of the target gas has an equipment (250) for cooling the HRS, before reaching the chambers.The apparatus (210) has an equipment for removing water from the HRS leaving the cooler, before reaching the sensor. The apparatus further has another sensor in the HRS, thermally active to the target gas.Preferred Properties: Sensor properties, such as resistance, conduction, impedance, temperature, voltage and/or amperes, are used to determine CO concentration.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The sensors in the chambers are biometric sensors comprising palladium, copper, molybdenum, calcium, cyclodextrins, chlorides, bromides and an acid, preferably a porous silica substrate coated with a chemical reagent of palladium salts, such as palladium sulfate, chloride and bromide; heteropolymolybdates, such as silicomolybdic acid, ammonium molybdate and alkali metal molybdates; copper salts, such as copper sulfate, chloride, bromide and perchlorate; alpha, beta, gamma or delta cyclodextrins and hydromethyl ethyl and propyl derivatives; and/or soluble salts of alkaline and alkali chlorides and bromides.The catalytic sensor comprises a nickel catalyst.