Provides details of a series of laboratory and site tests to determine the performance of a range of IAQ (indoor air quality) sensors. Presents the results of laboratory tests and site monitoring in three buildings. Discusses the correlation coefficients found. States the site monitoring demonstrated that the dilution of pollutants in the indoor environment may be carried out at the expense of introducing polluted air from the outside. A major source of pollution to affect the monitored sites was from vehicle traffic (indicated by levels of (CO). Notes that the use of CO2 controlled ventilation techniques is more effective than those using IAQ sensors in applications where IAQ is primarily influenced by varying occupancy.