This research assesses whether the perceived indoor air quality (IAQ) can be improved with additional sensors in older buildings. The research does not investigate IAQ in its broadest sense, but focus on phenomena perceived by the human senses, such as thermal comfort. The effects of the maintenance of technical systems on perceived IAQ are also studied. In the study, 2506 sensors were installed in 29 public buildings in nine cities in Finland. The change in studied indicators was measured over four years and compared to 65 buildings in the comparison group. The study provides an objective view of the usefulness of BAS-connected and cloud-based sensors. The study also shows that a building owner considering introducing cloud technology to improve perceived IAQ should also be prepared to reform property maintenance processes. The study showed that additional sensors connected to the BAS improve thermal stability. No such improvement was observed in sensors connected to cloud services.