As you seem unable to check the Yellow Pages

, the information (including a helpful map) can be found at its website: fire.com.hk
I think there are several reasons why smoke/CO2 alarms are not a legal requirement in domestic premises. One would be enforcement, the government has enough trouble trying to owners (particularly of really old buildings) to get up to the current safety codes. Developers don't want any other requirements; they managed to get the one about having windows in bathrooms ditched. And Hong Kong is also a fairly free city; it hasn't reached the nanny state status of the UK, for example.
