Sensor Electronics” full-flow gas detector measures carbon-dioxide levels at natural-gas wellsites, collection/distribution pipelines, separation stations, or treatment plants. The detector plugs directly into the pipeline, it continually measures actual CO2 levels in the gas flow, in contrast to conventional bypass sensors that simply sample a small portion of the gas. The detector requires no venting or flaring of waste gas. The detector sends a four to 20 mA signal, showing actual CO2 values at any gas flow, regardless of velocity, pressure, and/or concentration. The detector is also resistant to the effects of dust, dirt, oil mist aerosols, airborne contaminants, toxic/corrosive atmospheres, or temperature/humidity extremes. The detector measures 4.5 inches long, three inches wide, 5.5 inches high (including one-inch boss). Operating temperature range is zero to 150 F; humidity zero to 99 percent RH.