This additional module can detect temperature, humidity and CO² rate of a room. Convenient for a children's room, it reassures us about the air quality in the house. Namely with the Netatmo application on Android, it is possible to have as homepage readings of the probe. Very convenient! In the end, not that expensive for a little peace of mind. In addition to the batteries take a long time (I do not yet changed after 4 months) and the design is very nice.