We have always advocated wiring the smokes to a local lighting circuit. The thinking is that if the breaker trips, you'll know it. You may not know it if a dedicated smoke circuit trips. Example being ... residents are on vacation and a surge or short outage causes the breaker to trip. After a week or so the batteries are dead and the residents return unaware of the lack of protection. The question: (I have no access to NFPA 72) is this code or just something we have always done?
Documentation I have access to (Thanks Bob) is as follows:
NJ IRC 2015......R314.6 .....Wiring shall be permanent, and without a disconnecting switch other than those required for overcurrent protection.
2013 National Fire Alarm & Signaling Handbook Chapter 29
Basically says a good practice is to use a branch circuit that supply a lighting circuit.....Further into that text it alludes that some states & locals may require a dedicated circuit, consult AHJ. (Not complete text, as I am not a typist.)
Seems like a round about way of saying 'either or'; however here it is a dedicated circuit.