The Johnson Controls CD-P1000-00-00U Duct Mount CO2 Transmitter is an HVAC sensing device designed to measure carbon dioxide levels in air ducts and provide an output signal to building control systems. It uses a CO2 sensing element to monitor air quality and transmit accurate concentration data for ventilation control. This transmitter is commonly used with air handlers, rooftop unit... https://www.partshnc.com/cd-p1000-00-00u-johnson-controls-duct-mount-co2-transmitter