At a career fair in an auditorium I was showing a sensor suite with OLED displaying current readings, one of which was the SCD41 CO2 sensor (they cost more than the esp32!)

I watched the sensor rise from 800 to 1700 PPM by the time the last group left the

It’s quite easy to build one and deploy with esphome and breadboard with stuff you can order on Amazon and have an LLM walk your through hardware and setup.

It is interesting where the rate of speech quickens as the co2 rises and the body starts to notice the co2, or maybe that was just the coffee.