Abstract: A detection and control system based on ambient air quality is disclosed. The system sequentially monitors the ambient air quality in different locations of a building or the like, and controls other gases such as carbon dioxide present in a building. The system has at least one sampling head, with a pump associated with that head, a calibration pump, and a selector for selecting operation time of each pump in sequence, and time lapse between sequences. An analyzer analyzes samples of gas from each sampling head and the calibration pump, the analyzer produces an analysis signal representing quantity of contaminant gas present in each sample. Provision is made for setting a plurality of first predetermined set points representing levels of the contaminant gas which may occur in each sample, a plurality of on/off signals representing when the contaminant gas reaches the first set points are produced.