A car full of people can soon lead to the build-up of CO2 to a level where the driver can be come drowsy, creating a safety issue. Of course, it is possible to ventilate the cabin all the time but at full speed this is neither a comfortable nor an energy efficient option.
Monitoring the concentration of carbon dioxide in the cabin allows the ventilation to be controlled at the optimal level, preventing drowsiness.
Non-Dispersive Infrared (NDIR) spectroscopy is by far the most common gas detection method used today. Infra-red radiation generated by a broad band emitter is passed through the gas which is contained in a measurement cell.
The detector uses an IR filter with an appropriate wavelength transmission band to measure the strength of the absorption of the target gas. The strong absorption allows relatively low concentrations of gas to be detected with small path lengths and inexpensive components.