Not so much CO2 detectors perhaps but
CO detectors....we have these in our piston tin cans and houses - so why not in airliners?
CO is as likely, possibly even more so than Organo-Phosphates, to be the cause of fume events and the physical and neurological effects that ensue.
Also, there are much more modern and effective CO detectors than those bits of card with palladium sulphate that change colour. Modern detectors (alarms 100-400ppm) could be easily retrofitted to most modern airliners. Yes some issues with picking up fumes from nearby ac on ground - but once airborne, should not go off (WOW interlink?)
However, there are plenty other nasties created when aero-engine oil is pyrolised......not sure there is much research on this. However, the insidious effects of CO are well known
Footballer Emiliano Sala Crash Channel Islands