Short answer: Hardwired (240V) smoke alarms run on mains power with a backup battery and can be wired to go off together. They’re required in most new homes in NSW and recommended by Fire and Rescue NSW. 10-year lithium alarms run on a sealed battery, need no wiring and are quick to install, which makes them a common choice in existing homes and rentals. Both are legal in existing homes if they meet AS 3786 and are in the right places.
Choosing smoke alarms used to be simple: a 9V battery alarm in the hallway. Today you’ll be weighing up hardwired alarms, sealed 10-year lithium units, photoelectric sensors and wireless interconnection. This guide compares the two main types for NSW homes and helps you decide.
The quick comparison
| Hardwired (240V) | 10-year lithium (sealed battery) | |
|---|---|---|
| Power | Mains power with backup battery | Sealed lithium battery for the life of the alarm |
| Installation | Licensed electrician | Can be screwed to the ceiling without wiring |
| Interconnection | Wired or wireless, depending on model | Wireless interconnection on some models |
| Required for new homes in NSW | Yes, where mains power is supplied | No (only where mains power isn’t available) |
| Battery changes | Backup battery, depending on model | None; replace the whole alarm at end of life |
| Lifespan | Replace every 10 years | Replace every 10 years |
| Best for | Renovations, new builds, whole-home protection | Existing homes, rentals, quick upgrades |
What NSW rules say
In existing homes, NSW law requires at least one working smoke alarm on every level, as covered in our NSW smoke alarm rules guide. The alarms must meet AS 3786. Battery-powered alarms are allowed in existing homes.
For new homes, the National Construction Code housing provisions, with the NSW variation, require smoke alarms complying with AS 3786 that are connected to consumer mains power where it’s supplied, and interconnected where more than one alarm is installed. You can read the NCC 2025 NSW smoke alarm provisions. Major renovations may also trigger these requirements, so check with your certifier.
The case for hardwired
- No reliance on batteries. Mains power means the alarm keeps working even if nobody changes a battery.
- Interconnection. Many hardwired systems are linked, so a fire in the back bedroom sets off the alarm near the front door too.
- Recommended practice. Fire and Rescue NSW recommends hardwired, interconnected smoke alarms, and alarms in bedrooms, living areas and hallways.
- Good fit for renovations. If ceilings are open or you’re rewiring, adding hardwired alarms costs much less than retrofitting later.
The trade-offs: installation is electrical work, so you need a licensed electrician and a compliance certificate. In terraces with no roof access, cable runs can take longer.
The case for 10-year lithium
- No wiring. They can go up in minutes with no ceiling access needed.
- No annual battery change. The sealed battery lasts the life of the alarm.
- Wireless interconnection is available on some models, giving linked alarms without new cables.
- Good for rentals. Landlords avoid the yearly battery replacement that removable batteries need.
The trade-offs: when the battery runs low, you replace the whole alarm. Wireless interconnection usually depends on sticking with one brand.
Photoelectric is the sensor to look for
Whichever power source you choose, Fire and Rescue NSW recommends photoelectric alarms. They respond well to the smouldering fires common in homes and are less prone to nuisance alarms from cooking than older ionisation alarms.
Which should you choose?
Choose hardwired if
- you’re renovating, extending or rewiring
- your existing alarms are already hardwired (replace like for like)
- you want the most robust whole-home system
Choose 10-year lithium if
- your home has no easy ceiling access and no renovation planned
- you need a quick, low-disruption upgrade in a rental
- you’re adding extra alarms in bedrooms on top of existing hardwired ones (check compatibility)
Want hardwired alarms done properly? Our licensed electricians install and replace smoke alarms across the Inner West and lodge the compliance certificate. Call 0421 772 661.
Cost factors
We don’t publish fixed prices for alarms because jobs vary. The things that change the cost are:
- number of alarms and levels
- hardwired vs battery, and whether the home already has a smoke alarm circuit
- roof access and ceiling type
- interconnection (wired or wireless) and brand
- whether old alarms need removing and patching
As a typical national figure, hipages lists a hardwired smoke alarm installation at around $150. That’s a market average, not a Blue Link price.
We install alarms in Marrickville, Ashfield, Haberfield and surrounding suburbs.
Frequently asked questions
Are battery smoke alarms legal in NSW?
Yes, in existing homes, provided they comply with AS 3786 and there’s at least one working alarm on every level. New homes generally need mains-powered, interconnected alarms.
Do hardwired smoke alarms need batteries?
Most have a backup battery so they keep working during a power cut. Some use a sealed lithium backup that lasts the life of the alarm.
Can I mix hardwired and battery alarms?
You can have both in a home, but they won’t interconnect unless the models are designed to work together. Ask your electrician about compatible options.
How long do smoke alarms last?
Fire and Rescue NSW recommends replacing smoke alarms every 10 years, whatever the power source.