do smoke alarms need to be wired in or are batteries ok

Two separate questions get tangled together here. What a new or substantially renovated dwelling must have is set nationally through the building code. What an existing, untouched dwelling must have is set by each state and territory, and those rules have been moving.5

The distinction that matters

• Interconnected means when one alarm sounds, they all sound. This is the change that saves lives, because it wakes people at the far end of a house from a fire that started at the other end.
• Hard wired means mains powered with a backup battery, rather than battery only.
• Photoelectric describes the sensing type, which detects smouldering fires faster than the older ionisation type.

Where it differs most

Queensland has legislated the most extensive retrofit obligation in Australia, requiring interconnected photoelectric alarms in all dwellings, with staged dates by circumstance including sale and lease. Other states have their own positions, and several require alarms to be tested or replaced at defined intervals regardless of type. Because these dates have been amended repeatedly, check your own state's fire service or building regulator rather than relying on a summary.