The maintenance-free, microprocessor-controlled AERASGARD® RFTM - LQ - CO2 - Modbus and RCO2 - Modbus / RLQ - CO2 - Modbus with Modbus connection, with / without optional display, in an elegant enclosure, plastic, with snap-on lid, base with 4-hole attachment, is used to to monitor the entire room climate. For this purpose, measurands air humidity, temperature, CO2 concentration as well as air quality (VOC) are measured. By using a single device to monitor all four measurands, it is possible to effectively monitor and regulate the entire room climate. It measures CO2 in the range of 0...5000 ppm, VOC at one of three selectable sensitivity levels LOW / MEDIUM / HIGH, temperatures in the range of 0...+50°C, as well as relative air humidity from 0...100 % r.H. The relative humidity (% r.H.) quotient of water vapour partial pressure divided by the saturation vapour pressure at the respective gas temperature. A digital, long-term stable sensor used as measuring element for relative air humidity and temperature guarantees exact measurement results. The air quality is determined based on a (VOC) gas mixture sensor. The CO2 content of the air is measured using an optical NDIR sensor (non-dispersive infra-red technology).