Smoke Alarms in NSW: Wiring, Interconnection and AS 3786 Compliance
By ARCK Electrical ? Trade counter, North Parramatta ? Reviewed May 2026
Quick Q&A - click to expand
Are battery-only smoke alarms still legal in NSW? +
Only in existing dwellings without 240V smoke alarm wiring available. The replacement battery alarm must be a 10-year sealed lithium photoelectric unit complying with AS 3786 - not a removable-battery 9V alarm. For new builds and major renovations, the install must be 240V mains-powered with battery backup, hard-wired and interconnected.
Do alarms need to be interconnected? +
Yes for new builds and major renovations under NCC. When one alarm detects smoke, every alarm in the dwelling sounds simultaneously - gives occupants more reaction time, especially in larger homes where a fire in one wing might not wake someone sleeping in the other. Interconnection can be hard-wired (three-conductor) or wireless on compatible units.
What's the difference between photoelectric and ionisation alarms? +
Photoelectric alarms detect the larger smoke particles produced by smouldering fires (the most common real-world domestic fire). Ionisation alarms detect the smaller particles from flaming fires but are slower on smouldering and produce more nuisance trips near kitchens. NSW now requires photoelectric for new and replacement alarms. Ionisation alarms still in service can stay until end of life but must be replaced with photoelectric.
How often do smoke alarms need replacement? +
AS 3786 sets a 10-year service life on every alarm from the date of manufacture (printed on the unit), regardless of type. Test monthly with the test button, vacuum every 6 months, replace at 10 years or sooner if the alarm beeps end-of-life. Check the manufacture date when buying - a 'new' alarm that's been sitting in a warehouse for 3 years has only 7 years of useful service left.
Can I install smoke alarms myself? +
The hard-wired 240V installation is licensed electrical work in NSW - sparkie only. The 10-year lithium standalone alarm replacement (no electrical work) can be DIY for owner-occupiers in their own home, but landlords / property managers are responsible for compliance and most insure through a licensed electrician for documentation.
Smoke alarm rules in NSW have changed in stages over the past decade. The current state: photoelectric alarms compliant with AS 3786 are mandatory in every residential dwelling, with stricter requirements for new builds and major renovations. This is the trade reference for what you specify, where you put it, and how it's wired.
What NSW requires today
The legislative source is the Environmental Planning and Assessment (Development Certification and Fire Safety) Regulation plus the NCC (National Construction Code) Volume Two. The combined effect:
- Every residential dwelling must have working smoke alarms - owner-occupied, rental, holiday let, granny flat
- Alarms must be photoelectric type (ionisation alarms are no longer accepted for new installs)
- Alarms must comply with AS 3786:2014 (the construction and performance standard)
- New builds and major renovations require 240V mains-powered alarms with 9V battery backup, hard-wired and interconnected
- Existing dwellings without 240V smoke alarm wiring can use 10-year sealed lithium battery standalone alarms in place of mains-wired units
- Interconnection is required where multiple alarms are installed in a new build - when one alarm sounds, every alarm in the dwelling sounds
Where alarms go
Per AS 3786 + NCC, on a typical Sydney residential:
- Every bedroom - one alarm inside each bedroom
- Every hallway serving bedrooms - one alarm in the corridor connecting bedrooms (so a sleeping occupant is woken by an alarm in their path)
- Every storey - at least one alarm on every level, including basements and lofts that are habitable
- If no hallway/corridor exists between bedrooms and the rest of the dwelling, an additional alarm in the most-likely-path-of-travel
- Stairwells - at the top of any stairwell connecting habitable floors
Placement within a room:
- Ceiling-mounted preferred, at least 300mm from any wall or ceiling fan blade tip
- Avoid within 400mm of a corner, light fitting, air vent, or directly above a stove
- Bathrooms, ensuites, garages, laundries - generally NOT recommended (steam, exhaust, dust = false alarms). Hallway adjacent is the placement.
240V mains-powered with battery backup
The current spec for new builds and major renovations:
| Feature | What it means on the install |
|---|---|
| 240V mains-powered | Connected to a dedicated circuit (or shared with lighting on a sub-circuit) - not battery-only |
| 9V battery backup | Internal backup battery keeps the alarm running during a mains failure |
| Interconnected | Wired (or wireless) so all alarms in the dwelling alarm together when one detects smoke |
| AS 3786 compliant | Listed on the manufacturer's compliance certificate - check before fitting |
| Photoelectric | Detects smouldering fires effectively (the real-world risk in domestic fires) |
Interconnection is typically done by:
- Hard-wired interconnect: a third "signal" wire runs alarm-to-alarm. Limit per AS 3786 is usually 40 alarms per loop. Standard 3-core+earth TPS or specific smoke alarm cable works.
- Wireless interconnect: alarms with built-in radio modules pair on first power-up. Useful for retrofits where you can't run a third wire.
For a typical 3-bedroom domestic install, you'll fit 4-6 alarms on one interconnected loop powered from a dedicated lighting sub-circuit (usually 1.5mm? T&E on a 6A RCBO).
Smoke alarms + interconnect kits in stock
PSA Products, Quell - 240V photoelectric with battery backup, 10-year sealed lithium, wireless interconnect.
Browse fire safety ?When the 10-year lithium standalone alarm is OK
In existing dwellings without 240V smoke alarm wiring, NSW allows 10-year sealed lithium battery photoelectric alarms in place of mains-wired units. The alarm has a non-replaceable battery that lasts the full 10-year service life. After 10 years (or sooner if the alarm signals end of life), the whole unit is replaced.
This applies to:
- Pre-existing homes where retrofitting 240V wiring isn't practical
- Rental properties where the owner is replacing aged-out alarms but not doing major works
For new builds and major renovations, you can't use standalone alarms - the install must be 240V mains-powered.
Compliance note
Electrical work in Australia must be carried out by a licensed electrician under AS/NZS 3000. Smoke alarm circuit wiring, interconnection, and final-test commissioning fall within that. The placement decision (which rooms get alarms, ceiling spacing) is typically the installer's responsibility but the design rules in AS 3786 + NCC must be followed.
Order from ARCK
We stock the PSA Products and Quell smoke alarm range - 240V photoelectric with battery backup, 10-year lithium standalone, and wireless interconnect bases. Same-day pick-up from North Parramatta.
Browse the fire safety range, pair with the matching circuit protection for the alarm circuit, or call the counter on (02) 9890 9693 for spec assistance. Mon-Fri 6:30am-5pm, Sat 7:30am-1pm.