The word most people miss is “every”
The rule is not “one in the hallway”. It is one in every corridor or hallway associated with a bedroom. In a plain three-bed house with all the bedrooms off one hall, that is one alarm and everyone gets it right. In a house where the main bedroom sits off the living end and the kids are down the other end, it is two — and that is the house people get wrong.
The second half catches the other common miss: each other storey not containing bedrooms. A downstairs with no bedrooms still needs an alarm. So does a walk-in basement. The stair is how fire travels and a house with all its alarms upstairs is a house that finds out too late.
Queensland counts differently, and it has a deadline
Queensland is the only place in Australia that requires an alarm in every bedroom as well as the hallways and the storeys — and the only place where the requirement is retrospective. Every existing private home, townhouse and unit needs interconnected photoelectric alarms by 1 January 2027.
That is why the same four-bedroom house is 2 alarms in Sydney and 6 in Brisbane. The Queensland number is not a recommendation you can take or leave.
| The same house | NSW, VIC, WA, SA, TAS, ACT | Queensland |
|---|---|---|
| Single storey, 3 beds, 1 hall | 1 | 4 |
| Two storey, 3 beds up, 1 hall | 2 | 5 |
| Two storey, 4 beds over 2 halls | 2 | 6 |
| Two storey, beds both levels, 2 halls | 2 | 2 + every bedroom |
Interconnection is the part that costs money
NCC 9.5.1(d) requires alarms to be interconnected where there is more than one — when one sounds, they all sound. Whether that applies to your existing house depends on your state and when the home was built, and the honest answer is that it is retrospective in Queensland and tied to new builds or renovations nearly everywhere else.
Interconnection usually means an electrician, because 9.5.1(c) also requires alarms to be powered from the mains where mains power is supplied to the building. The exception that saves people money is the wireless interconnected type with a sealed ten-year battery, which is why Queensland allows either route.
The state-by-state rules checker is where the type, power and interconnection answers live. This page only counts them and places them.
Two worked examples
A two-storey Sydney house: three bedrooms upstairs off one hall, nothing downstairs.
- Hallways serving bedrooms: 1
- Storeys with no bedrooms: 2 − 1 = 1
- Required: 2 alarms — one in the upstairs hall, one downstairs
- Recommended on top of that: one in each of the three bedrooms, so 5
The same house in Brisbane, single storey, three bedrooms off one hall.
- Hallways serving bedrooms: 1
- Storeys with no bedrooms: 1 − 1 = 0
- Queensland adds every bedroom: +3
- Required: 4 alarms, photoelectric, interconnected, by 1 January 2027
Where they actually go on the ceiling
- On the ceiling, away from the corner. Air does not move in the corner where the ceiling meets the wall, so an alarm there sees smoke late. Western Australia sets 300 mm as the minimum distance.
- Not right beside the kitchen or the bathroom. Toast and steam cause nuisance alarms, and a nuisance alarm is an alarm somebody takes the battery out of.
- Not in the path of a fan or an air conditioner outlet. Moving air pushes smoke away from the sensor.
- On a sloped ceiling, near the high point but not in the apex. Follow the manufacturer’s instructions — the Code points at them and so does every state.
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General information for Australian homeowners and trades, and an estimate only — not legal advice, and not building or fire-safety advice, and not a compliance certificate. The count uses the national baseline in NCC 2022 Housing Provisions clause 9.5.2, read 3 September 2026, plus the Queensland and Northern Territory additions from their own regulators. Your state can be stricter than the baseline and your council stricter again, and this page does not cover alarm type, power source, wiring or maintenance duties, which differ by state and by when the home was built. Hardwired alarms are licensed electrical work. No regulator has reviewed this page.