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.
Smoke detectors frequently work by having a teensy little radioactive emitter and a teensy radioactivity detector somewhere close to it. It works a bit like a laser trap in a video game or movie, if you break the laser-beam by walking through it, it triggers the alarm because the detector can no longer see the beam.
But it doesn’t have to be smoke. Water particles will do it, dust can do it, especially when there’s construction work going on putting the dust in the air… it doesn’t matter. It just needs to be enough to break the connection between emitter and detector.
Wet steam and the vapor from humidifiers is pretty effective at triggering it because the droplets are bigger than regular humidity.