Air quality sensor for measuring CO2, mixed gas (VOC), temperature and humidity outdoors and in areas requiring high IP protection class (e.g. subway stations, tunnels, exhibition halls, cooling and greenhouses as well as in production halls and warehouses). If required, default values can be adjusted via Thermokon USEapp. For devices with CO2 and VOC, each output can be configured to be a mixed output (selectable signal ratio between CO2 and VOC). Devices with a relay option can be used as 2-point controllers or 2-step controllers.