> Obviously it could also be Invisible Evil Gas Traces, and the impact of being wrong is severe, so I wouldn't blithely dismiss the alarms as planned obsolescen

> Obviously it could also be Invisible Evil Gas Traces, and the impact of being wrong is severe, so I wouldn't blithely dismiss the alarms as planned obsolescence either. And that is why I only buy CO alarms which display the ppm they measure. "I'm out of sensor lifetime / battery, please replace me" is a very different level of priority than 300ppm CO. And how I react to 300ppm is very different from how I would react to 3200ppm.