We did the same, it's very noticeable, what we sometimes do is cover it and if people are feeling drowsy only then reveal it so we could be sure it wasn't a placebo (it wasn't).
I hacked up (I'm not a programmer!) some code to log the data to CSV, which I then presented to the business as a case to change our aircon system: https://github.com/sammcj/airqualitylogger
In both the OP and your comment I initially interpreted "CO2 monitor" as a computer display that emits CO2. I was wondering how this would boost your productivity for a confusing 10 seconds.
Yeah, it didn't need new all new Aircon but we got the Aircon techs in to look at it and they're changing where the inlet vents are located and adding an additional unit of separation into the ducting.
We did the same, it's very noticeable, what we sometimes do is cover it and if people are feeling drowsy only then reveal it so we could be sure it wasn't a placebo (it wasn't).
I hacked up (I'm not a programmer!) some code to log the data to CSV, which I then presented to the business as a case to change our aircon system: https://github.com/sammcj/airqualitylogger