Selecting the right CO2 sensor depends on the application. If the monitored environment experiences periodic exposure to background CO2 levels, the optimal solution will be a “single-channel” NDIR sensor utilizing ABC Logic^TM . This sensor will provide in situ automated recalibration for the life of the sensor, improving performance and reducing the cost of ownership. If the monitored environment is continually occupied or not expected to see diurnal CO2 concentration cycles (such as hospitals, detention facilities, and indoor agricultural structures) a “dual-channel” NDIR is necessary. Without periodic exposure to background CO2 levels, firmware-based algorithms cannot be reliably deployed for “drift” compensation. While the hardware-based reference inherent in the “dual-channel” NDIR sensors can provide excellent “drift” compensation, recalibration will eventually be required for these NDIR sensors in order to retain factory-performance specifications.