Smoke alarms buying guide: Types, features, and installation tips

Our previous testing showed little difference in how quickly photoelectric alarms from different manufacturers respond to smoke, so we don’t currently test them. We continue to monitor the market for developments and to provide up to date buying advice.

So what type of smoke alarms should you get? Where should they be installed? What responsibilities do landlords and tenants have? And how often should you maintain and replace alarms?

Types of smoke alarms

Smoke from a flaming wastepaper bin or cooking oil fire is different to smoke from smouldering upholstery foam, bedding, or the plastic parts in electrical equipment. But both types are deadly.

Photoelectric smoke alarms are good at detecting both flaming and smouldering fires. They’re the type recommended by Fire and Emergency New Zealand.

A few years ago, we reported that ionisation smoke alarms are much slower at responding to smouldering fires than photoelectric ones. They've subsequently been removed from sale in New Zealand. Double-check you’re getting a photoelectric alarm when you buy, especially if ordering from overseas.

If your home still has ionisation smoke alarms (they’ll have a radiation symbol somewhere on the plastic body), replace them with photoelectric ones.

There are also thermal heat alarms, carbon monoxide alarms and others. These are not smoke alarms so should not be used as a substitute. However, some smoke alarms include one of these additional functions.

Hard-wired smoke alarms

Hard-wired photoelectric smoke alarms are the best choice because they’re connected to your home’s 240V power supply and have a back-up battery in case there’s a power cut.

Back-up batteries are either 9V (which need replacing each year), or rechargeable. Rechargeables last the life of the smoke alarm (10 years) and automatically recharge via the 240V power supply.

Installation and replacement of hard-wired alarms must be carried out by a licensed electrician, which can be costly. So, if you’re renovating, take the opportunity to install alarms at the same time. Consider a set of interconnected alarms.

Battery powered smoke alarms

If you’re not ready to go hard-wired or have areas where it’s not possible, battery powered smoke alarms can be installed anywhere and by anyone. Their batteries are either:

• Built-in, sealed lithium-ion. They have a life of about 10 years. When they run flat, the whole smoke alarm should be replaced. They cost about $20+.
• User replaceable, usually 9V. These batteries last about one year in a smoke alarm. The unit will start chirping to indicate when the battery is getting low – typically in the middle of the night when it’s colder. They cost about $10+.

We recommend any battery powered smoke alarms have a built-in 10-year lithium-ion battery. Alarms with user replaceable batteries might seem cheaper initially. But a good 9V lithium battery costs about $22 making this type less economical over time with annual replacement required.

In addition, yearly middle-of-the-night ‘low battery chirps’ can be frustrating, causing people to remove batteries before they’ve bought a replacement – leaving them at risk.

Interconnected smoke alarms

Some smoke alarms can be connected via hard-wiring or wireless technology. Smoke detected in one area will trigger all connected alarms at the same time so there’s no delay to anyone being alerted. This is especially important in large or multi-level homes. And from November 2024, it’ll be a legal requirement for newly built housing units.

Smoke alarms for the hearing impaired

For the hearing impaired, Fire and Emergency New Zealand recommends a hard-wired series of interconnected photoelectric smoke alarms fitted with bed shakers, strobe lights and/or pagers.

These systems can be expensive. But some people will be eligible for either funding from the Ministry of Health or for a system to be installed by Housing New Zealand. Contact Deaf Aotearoa to learn more.

Smoke alarm features

All smoke alarms have a test feature and a hush button.

The test feature allows you to check whether the alarm is working, usually by the press of a button. Some models can be tested by shining a torch over a sensor.

Pressing the hush button will silence an unwanted alarm without having to remove the battery.

Some smoke and combination (for example, smoke and carbon monoxide) alarm systems have additional features such as a remote-control test and silence function, phone notifications, and motion-activated night lights or escape lights that come on when the alarm activates.

Smoke alarms also come in micro sizes or with a recessed design. There’s no obvious difference in performance between different sized alarms.

Where to fit smoke alarms

You should install an alarm in every bedroom and hallway.

Alarms must be installed on or near the ceiling because smoke rises. There’s evidence that a downstairs fire is likely to trigger an upper stairwell alarm before one fitted downstairs.

Avoid installation close to kitchens, bathrooms, heat pumps and air vents (see our tips on preventing false alarms below).

New Zealand law states that smoke alarms must be installed:

• in all residential buildings, including rental homes, boarding houses, rental caravans, and self-contained sleep-outs;
• on each level of a multi-level home;
• in every escape route (hallway); and
• within 3m of each bedroom door or inside every room where a person sleeps.

Fire and Emergency New Zealand also recommends smoke alarms for living areas.

Landlord and tenant responsibilities

It’s the landlord’s responsibility to install working, unexpired smoke alarms in rented properties and make sure they keep working. The alarms must:

• be photoelectric;
• comply with Australian Standard AS 3786 or one of these equivalent standards: UL 217, CAN/ULC S531, BS EN 14604 or ISO 12239;
  
• have a hush button to temporarily silence them in case of a false alarm; and
• be installed according to the manufacturer’s instructions with the replacement date on display.

In addition, from November 2024, the smoke alarms installed in newly built housing units must be interconnected (where more than one alarm is required).

It’s the tenant’s responsibility to regularly test smoke alarms and replace batteries (if user replaceable) and let the landlord know if there’s a problem with any smoke alarm.

Preventing false alarms

Nuisance alarms aren’t just a response to burning toast. They can also be caused by high humidity, dust and insects. Every alarm has a hush button, but the alarm will sound again unless the cause is removed.

Frustration from false alarms often results in batteries being removed. Then, if there’s a real fire, you’ll be at risk.

Minimise false alarms by:

• avoiding installation within 3m of the kitchen or bathroom;
• positioning smoke alarms away from heat pumps and heating vents that stir up dust;
• using an extractor when cooking and showering, and keeping doors closed; and
• vacuuming your alarms occasionally to remove dust and trapped insects.

Maintenance and replacement

Test and vacuum your smoke alarms monthly. Pressing the test button should make the alarm sound briefly. If it doesn’t, it’s time to replace your battery or smoke alarm.

Replace 9V batteries every year or sooner if an alarm is chirping. Set an annual diary reminder and/or choose a date you’ll remember, such as the end of daylight savings. Consider upgrading to smoke alarms with a built-in 10-year lithium-ion battery or, better still, a hard-wired set of interconnected alarms.

Replace all smoke alarms within 10 years. Over time, all types of smoke alarms have an increased risk of malfunction due to a build-up of dust and insects or from corrosion of the electrical circuitry. Check the use by date or date of manufacture and replace within 10 years – sooner if the unit indicates the battery is running low.

Fire safety tips

In addition to having enough of the right type of smoke alarms installed and maintained:

• Consider a fire blanket or fire extinguisher for the kitchen. They can be used to smother a small cooktop fire before it gets out of control. They shouldn’t be used to tackle larger fires. Make sure they’re easy to access and you know how to use them.
• Have an escape plan so everyone knows the best ways to evacuate and where to meet outside. Practise your escape plan every 3–6 months. You can make your three-step plan online at Fire and Emergency New Zealand.