Amprobe CO2-200 Wall-Mounted CO2 Meter Wall-mounted digital meter measures ambient level of carbon dioxide (CO2) to monitor indoor air quality and performance of heating, ventilation, and air-conditioning (HVAC) systems Displays current CO2 levels, long-term average CO2 levels measured over an 8-hour period, and short-term average CO2 levels measured over a 15-minute period Alarm notifies operator when CO2 levels reach or exceed a preset threshold When connected to a building's HVAC system, the meter's built-in relay activates the HVAC system if CO2 levels reach or exceed the alarm's upper-limit threshold Liquid crystal display (LCD) shows ambient CO2 levels, as well as air, wet bulb, or dew point temperature and humidity CO2 measurement up to 9999 ppm, temperature, relative humidity, dew point and wet bulb High performance low drift sensor designed with NDIR (non-dispersive infrared) waveguide technology with automatic background calibration Audible alarm threshold setting to setup warning against carbon dioxide level with output drive relay to control air flow system Recording of maximum, minimum and average values with recall function Meter, manual, power adapter 100-240V AC