I have a back bedroom with sealed windows, and it gets dry sometimes. It’s for a person with horrible allergies. This room is so clean you could eat off the floor so to speak. I run a humidifier set to 60% with distilled water for the person in there. When I checked on it last night to see if it needed to be filled, the humidity had gone up to 82%. This was because a ceiling fan had been left on and the sensor in the humidifier wasn’t getting correct data from the moving air (I think). My hallway smoke / Co2 detector went off as soon as I opened the bedroom door. It would not clear until I pointed a hair dryer at it, then it shut the hell up.
TLDR: My smoke detector doesn’t like humidity all of a sudden?? and went off and would not clear. It has been more humid than that in the entire house without humidifiers running, and I have the same detectors in other locations with no issues.
So it's the smoke detector, not the CO detector? These are separate devices. A smoke detector will typically be on the ceiling and a CO detector will typically be close to the floor.
I've had smoke detectors which are set off by steam, such as from a hot shower. You can replace it with a style of detector which operates differently, not using photoelectricity to be triggered. Keeping batteries fresh is also supposed to help, but I don't know if it really does.
That said, you may want an alarm for humidity because 82% is quite high and may cause damage to the home.
If you're referring to Carbon Monoxide detectors [I recognize the OP made an error calling them CO2] commonly referred to as "smoke/CO", then, in the US at least, smoke and Carbon Monoxide detectors are usually combined units. I've never found one to be separated like that. A common example is below. Carbon Monoxide is similar, if not lighter than common air density, so putting one on the floor wouldn't make any real difference.
https://www.firstalert.com/us/en/products/alarms/combo-smoke-carbon-monoxide-alarms/prc710-10-year-battery-combination-smoke-carbon-monoxide-alarm-prc710/
Huh. I'm in the US, and have always had these as separate units because smoke detectors function best on the ceiling and carbon monoxide detectors function best by the floor (allegedly).
How weird, I've never seen that configuration. Today I learned. I just wanted to add that in case anyone read that and thought their living space was unsafe with a combination detector. The EPA says, if they are CO specific, to put them about eye level from the floor, or on the ceiling.
https://www.adt.com/resources/carbon-monoxide-detector-placement#:~:text=Carbon monoxide is lighter than,them on the ceiling%2C too.