Any existing smoke alarm being replaced from 1 January 2017 must be photoelectric-type alarms which complies with AS 3786-2014
If a smoke alarm which is hardwired to a domestic power supply needs replacement, it must be replaced with a hardwired photoelectric smoke alarm.
In existing domestic dwellings, it is possible for have a combination of smoke alarms (240v and battery operated) and inter connectivity can be both wired and /or wireless.