A method of controlling air quality in an indoor environment of a building is described. The method utilizes a system that comprises a carbon dioxide sensor configured to detect an instantaneous value of carbon dioxide concentration in the air of the indoor environment of the building, a control unit in signal communication with the carbon dioxide sensor, a communication unit for establishing signal communication between the carbon dioxide sensor and the control unit, and a storage unit in signal communication with the control unit. The method comprises the steps of: a) defining and storing in the storage unit, by the control unit, control values of carbon dioxide concentration; b) detecting, by the carbon dioxide sensor, an instantaneous value of carbon dioxide concentration and sending, by the communication unit, the instantaneous carbon dioxide concentration value to the control unit, c) processing, by the control unit, the control values and the instantaneous values of carbon dioxide concentration to generate an output signal representative of the processing performed by the control unit; and d) sending, by the control unit the output signal to a visual and/or acoustic warning unit.