There has been an ammendment to the Electrical wiring rules AS3000-2018 which is to be mandatory from November 1st 2021 which will affect many domestic installations including smoke alarm upgrades.
Smoke alarms are to be regarded as lighting points and will require a safety switch protecting the hard-wired alarms if not already present when additions are made.
If the upgrade to the smoke alarms is done before November 2021, then this makes no difference until any alterations to smoke alarms, lights & fans are made at that property after that date.
If the upgrade to the smoke alarms at the property is done after that date, and there is existing wiring to hard-wired alarms that have no safety switch on the supply circuit, then there will be a need to install an additional safety switch at a smoke alarm upgrade would the existing circuit not be found to be protected.
This can add between $169-$250 depending on the switchboard having capacity.