Because smoke detectors don't detect smoke, they detect an interruption in a signal, either optical or electrical depending on type.
Guys right. Sometimes the detectors have an IF, or some other sort of light beam which reflects between two mirrors. If the signal is broken by any means the alarm will go.
Saying all that, I'v got an alarm outside my bedroom. Kept going off. Couldn't even vape in the house!!! That was mtl. Cloud chasing from from downstairs would set it and my bath water.
Dude came and replaced it and it had new batts. Not a problem at all now. Could just need new batts?
Found this. Some more than others
Which types of fire alarm are vulnerable to vapour?
There are different kinds of fire alarms, and some are more likely to be set off than others.
Ionisation: Sensitive to small particles of smoke. They utilise two electrically charged radioactive plates. When smoke particles enter the fire alarm they disrupt the electricity between the plates, setting off the alarm. This was the type used in our little experiment!
Optical alarms: Optical alarms work by beaming infrared light. When smoke particles enter the smoke alarm, the particles cause the infrared light to be scattered onto a light detector which triggers the alarm.
Heat alarms: Used in kitchens, these are unlikely to detect vapour as they are responsive to heat rather than to smoke.
When we spoke to South Wales Fire and Rescue Service, they told us that optical alarms are the type most likely to be set off by electronic cigarette vapour, although as our little experiment showed ionisation alarms can be set off too.
