I think we are talking about a CO detector, not a CO2 detector. My Designer has a combination CO/Propane detector that was out of date when I bought it. My dealer replaced it with a new one and it failed after 3 years. The failure mode was it going off in the middle of the night. Typically around 3:00am. It was replaced after a thorough check for leaks and no problems since.
I don't think these detectors are very high quality so infant mortality seems to be frequent. I just wish the combination CO/Propane detector was cheaper when it does fail.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof