The innovative idea of the company Simply Home is to contribute to get buildings healthier by developing and testing CO2 smart sensors in a preliminary study to deal with the air quality concerns in real-time, mainly in well insulated modern buildings not equipped with mechanical ventilation. Furthermore, these sensors could be integrated with other sensors developed by Simply Home for people's presence monitoring, as well as air temperature and humidity. Such monitoring sensors would be connected to a cloud-based smart system to manage autonomously the building or provide feed-back to the occupants' in real-time. On a longer time frame, the focus will be set on development of an advanced control and feed-back system based on smart algorithms for autonomous energy efficiency and indoor environment optimization. On one hand, the windows could be opened to promote a good air quality, however, the increase of natural ventilation can lead to a negative effect on thermal comfort and building energy demand. On the other hand, if the windows remain closed the thermal comfort is maintained, although the air quality decreases. The smart system would pretend to comply with a trade-off between energy and indoor environment conditions, while dealing with the users’ preferences and habits, as well as giving them feedback and recommendations to improve their use of the building.