How useless are these things?
I mean without any doubt they are helpfull if you are living in a big house full with furniture or in a couple of storeys tall apartment house but for sure not in a small 1 room bungalow in Thailand, where everything is made from stone and the bed is the only thing can burn, if you dont feel the pain from the fire, i doubt you will hear the alarm of a smoke detector.
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Airbnb should work on that issue.
Not ALL houses need this things like not ALL houses having bathtubs, which not mean they dont have a bathROOM