Wall mount CO2 sensors and transducers are intended to be mounted on a wall within the space being monitored or controlled. Features include: multiple CO2 display options including, No display, LCD display, or visual limit indicator (VLI), output options including 0-10 V, 0-5 V, 4-20 mA, and relay outputs, zero maintenance self-calibration via patented ABC Logic, optional built-in relative humidity and passive temperature sensing, finally, a European enclosure option.