The NDIR vs. eCO2 Deception
Many inexpensive smart air quality monitors advertise carbon dioxide tracking, yet show wild, erratic swings whenever someone opens a bottle of wine or cuts an onion. This happens because budget devices do not contain a real CO2 sensor—they use a cheap Metal Oxide Semiconductor (MOX) sensor to calculate 'estimated CO2' (eCO2).
How True NDIR Sensors Work
Non-Dispersive Infrared (NDIR) sensors pass a precise beam of infrared light (4.26 µm wavelength) through a miniature optical chamber. Because CO2 molecules absorb infrared radiation specifically at this frequency, the photodetector measures exact carbon dioxide molecules without being fooled by other gases.
Why MOX 'eCO2' Sensors Fail
MOX sensors measure total electrical resistance across a heated metal oxide film when exposed to volatile organic compounds (hydrogen, alcohol, VOCs). The device then uses an arbitrary mathematical algorithm to guess what CO2 might be based on ambient VOCs. If someone breathes near it or paints a wall, the eCO2 reading can spike from 600 ppm to 3,000 ppm instantly despite normal CO2 levels.