I would imagine it's still relative unlike temperature on the wrist (which is too affected by body temp)
That's the same area we inhale from... Wouldn't be right to measure there then? It's not like we're interested in the amount of CO2 on the ground (in this discussion)
It is not possible to come up with a different baseline for wrist-worn monitors because the measurements could change significantly based on even small factors like the position of the wrist or smartphone.
It would be like the weather station telling you it was 160 degrees outside because they put their thermal sensor on the asphalt, but you wanted to know the air temperature.
The CO2 content is a single chemical species within a mixed gas. Any air currents will cause mixing. Otherwise it undergoes diffusion which is actually a fairly slow process, although much faster in gases than in liquids.
I’ve done development on products with CO2 sensors and I’ve spent a lot of time with them on my desk right in front of me and also off to the side. Readings right in front of me are predictably higher.
You can breathe into a CO2 sensor 18 inches from your mouth and watch the values spike upward.
And, spoiler alert: if the entire area in front of you has an increased CO2 concentration, then your environment has an increased CO2 concentration. That’s the entire point.
Suffice to say I disagree strongly with both the argument that this would lead to hugely erroneous readings and also with the notion that people would panic.