[mrsteveman1]

> NDIR based CO2 (ex. Sensirion SCD31 or 41) also work fine.

SCD4x series are photoacoustic rather than NDIR, but they are true CO2 sensors and seem to work rather well given the size.

[s0rce]

I guess, yes and no. Technically the scd41 emits IR, it just doesn't detect transmitted light, instead sound produced by the CO2 that absorbed the light.