The MonkMakes Air Quality Kit for micro:bit is based around the MonkMakes Air Quality Sensor. This add-on for the BBC micro:bit measures the quality of the air in a room - how stale the air is. The outputs of the Air Quality Sensor board are analog: one for temperature and one for eCO2 (estimated carbon dioxide). These outputs can be read by a micro:bit and either displayed, for instance, as an air quality meter or logged over a period of time for all sorts of interesting experiments.
As well as the Air Quality Sensor itself, the kit also includes a set of alligator clip leads to connect it to the micro:bit and also a Speaker for micro:bit that can be connected to provide a warning of low air quality. A full color 24 page booklet of instructions is also included.