An alarm which speaks to you before it screeches at you, Nest Protect is designed to keep its cool in a crisis.

Australian homes must have smoke alarms installed by law, but when you can pick up a basic smoke alarm for $20 you're entitled to ask why you'd spend $189 for a luxury model. They all sound the alarm when they detect smoke, but the Nest Protect offers a few extra features which might save the day.

You've a choice of mains-powered or battery-powered Nest Protect alarms, the former should be installed by an electrician and comes with three AA lithium batteries to ensure – just like a standard smoke alarm – it keeps working if the power is cut.

Apart from detecting smoke, Nest Protect alarms also check for odourless carbon monoxide – which can build up to lethal levels if your home has faulty or improperly installed fuel-burning appliances such as wood fireplaces and furnaces, or gas appliances likes heaters, ovens and cooktops.

Despite ongoing debate carbon monoxide alarms are not required by law locally, but faulty gas heaters have claimed lives in Australia so you can't deny it's a real safety issue. That said you can pick up a basic CO alarm for $40, or a combined smoke + CO alarm for $60, so what makes Nest Protect worth more?

Fast and slow burns

Smoke alarms rely on photoelectric and ionising sensors – the former of which is better at detecting slow, smouldering fires. Ionising sensors are better at detecting fast-burning house fires, but are also more prone to false alarms. Some smoke alarms only use one type of sensor, while others use both.

These second-generation Nest Protect alarms on sale in Australia feature a "Split-Spectrum" photoelectric sensor which claims to detect both fast and slow-burning fires, along with a humidity sensor to reduce false alarms from bathroom steam.

This level of sensitivity means Nest Protect alarms can speak to you calmly when they detect an issue which hasn't yet reached the threshold at which, by law, they must sound the screeching alarm. You'll hear something like: *Bong* *Bong* *Bong* Please be aware, there is smoke downstairs. The alarm may sound, the alarm is loud.

The alarm knows the smoke is "downstairs" because you allocate each alarm a name as part of the set-up process (which requires an iOS or Android device).

If you have more than one Nest Protect they can talk to each other, even if the power is out and your WiFi network is down, so one-by-one they'll repeat the same warning around your home including the location of the incident – something which I tested for myself after reading conflicting reports as to whether this feature works when your WiFi is out.

If your WiFi is still running the alarms also send an alert to the Nest app on your phone, which is important if you've left children or pets home alone.

The spoken warnings might be enough for you to catch whatever triggered the alert before it escalates, such as something burning on the stove, but if the situation gets worse the alarms start to screech – once again triggering every Nest Protect alarm around your home rather than just the one which detected smoke or carbon monoxide.

You can silence the alarm by pressing the large button in the middle of the unit, which is much easier to press on the ceiling with a broom handle than the tiny reset button on your typical smoke alarm. Alternatively you can silence the alarm using the Nest app.

Put to the test

Putting smoke alarms to the test at home is obviously tricky, so to see them in action I lit a match about six inches below the Nest Protect and let the match burn down.

The Nest Protect waited about 30 seconds before issuing a spoken "Please be aware, there is smoke downstairs" alert. The upstairs Nest Protect repeated this warning, plus a notification popped up on my phone. As the match produced more smoke, the full alarm kicked in.

The same test on the HPM Professional smoke alarms already installed in my home – which use a combined ionisation and photoelectric sensor – saw the smoke alarm respond more quickly with the typical loud screeching. The other HPM Professional alarms around the house naturally remained silent.

If you live in a narrow three-story house like me, you can obviously see the appeal of having the alarms outside the bedrooms on the top floor trigger when there is smoke on the bottom floor, and vice versa.

Get smart

Apart from working in unison, the Nest Protect alarms also interact with other Nest smart home gear if they're still connected to the internet.

If you own Nest Cam security cameras, they'll automatically start recording when an alarm sounds to capture the event and thankfully Nest Protect doesn't rely on a Nest Aware monthly subscription to access its advanced features. Meanwhile if you've imported a Nest thermostat, it will automatically shut down your heating to slow the spread of fire and smoke throughout your home.

Unlike a basic smoke alarm, each Nest Protect runs a self-diagnostic each day to check the sensors, alarm, speaker, battery level and WiFi access. It also runs a monthly audio test, you can select the rough time of day and the alarm will calmy notify you before it tests the alarm.

Of course you're supposed to manually test all home smoke alarms regularly, but chances are you don't.

To reassure you that all is in order, the light on the Nest Protect turns green each night after it's completed its tests. Alternatively it glows yellow if there's an issue and you're sent a message, but should the battery level fall too low it will eventually speak to you about it and start chirping like a typical smoke alarm.

The light can also glow white to act as a night light, either running constantly when the lights are out or triggered by movement when someone goes to the bathroom in the middle of the night.

So what's the verdict?

At $189 each the Nest Protect isn't cheap but it's obviously hard to put a price on safety – especially if you're looking for an alarm that can stay cool in a crisis if you've got young children or elderly people in the house.

The cost might not seem so bad if you're installing them as part of building or renovating, with an electrician already onsite, plus it's easier to justify the expense if you'd benefit from a carbon monoxide alarm and remote alerts. They say you should replace your smoke alarms every ten years, so if yours are living on borrowed time then Nest Protect might make a wise investment.