Checks for Carbon Dioxide (CO2) concentrations. Maintenance free NDIR (non-dispersive infrared) CO2 sensor. Indoor Air Quality displayed in ppm with Good (380 to 420ppm), Normal (<1000ppm), Poor (>1000ppm) indication. Visible and Audible CO2 warning alarm with relay output for ventilation control. Measurement ranges: CO2: 0 to 9,999ppm. Temperature: 14 to 140 F (-10 to 60 C), Humidity: 0.1 to 99.9 percent RH. Displays Year, Month, Date, and Time. Max/Min CO2 value recall function. Automatic Baseline Calibration (minimum CO2 level over 7.5 days) or manual calibration in fresh air. Complete with Universal AC adaptor.