Humans respirate Volatile Organic Compounds (VOCs) as well as CO2. The BAPI sensor is able to measure these VOCs and indicate when a space is occupied just as well as a CO2 sensor. The advantage of the VOC sensor is that it measures air contaminants from other sources besides respiration, such as building materials, cleaners, perfumes and furniture and carpet off-gassing. Using this sensor for Demand Controlled Ventilation then is a way of achieving true indoor air quality, rather than just CO2 dilution. A further benefit is that it requires no additional work on your part. That's because the sensor converts the VOC reading to a CO2 equivalent level. This lets you use ASHRAE's CO2-based VRP schedule to ventilate. The BAPI-Stat "Quantum Prime" Unit Without Display comes with VOC, temperature and humidity sensing. The VOC level is indicated as "Good, Fair or Poor" by three discrete green, yellow and red LED's on the front of the unit.