21 Jul, 2022
Posted by Prime Time Electricians
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How Do Smoke Alarms Work?

A smoke alarm is the first and best way to alert the occupants of a building to the presence of a fire. They are an essential part of fire safety as they are active at night when your family is asleep.

Of course, there are more ways to protect yourself from a house fire than just smoke alarms. However, not only are smoke detectors the most effective, knowing how they work can hugely improve the effectiveness of these other methods. So how do smoke alarms work?

How do smoke alarms work?

There are different types of smoke alarms, with the two main types in Australia having either ionisation detectors or photoelectric detectors. There are significant differences between the two types of smoke detectors.

1. Ionisation

Ionisation smoke alarms are set off by large amounts of very small particles. To produce the amount of smoke needed to set off an ionisation alarm a situation with flaming fires will be needed. The smoke particles from a smouldering fire will not set them off, so an ionisation alarm will only detect established fires.

In addition to this, ionisation alarms are far more prone to false alarms set off by steam and other vapours from kitchens. Because of all this, ionisation detectors are considered to be the less effective of the two types, and should not make up the majority of the smoke alarms found inside your home.


Photo-electric smoke detectors, meanwhile, are set off by large particles in the air. As most modern furniture contains materials that give off large particles when burnt, it makes it easy for a photoelectric alarm to detect it.

The other main advantage of photo-electric alarms is that they can detect smouldering fires sooner, before they become full on and flaming, giving the building’s occupants a better and longer opportunity to reach safety.

Battery vs hardwired?

A hardwired smoke alarm is the most sure way to protect your home from fires. Battery-powered smoke alarms have a limited lifespan, like most electrical devices. Most of these smoke alarms will last up to ten years, but they may fail sooner. This is why testing them often is very important.

A mains-powered alarm will not run out of power, and does not require the user to remember to change the battery. Regarding which type to install, the law mandates that mains powered alarms be installed in houses that fall into the following categories:

  1. Is newly built since 1 July 1997.
  2. Has undergone significant renovations since 1 July 1997.
  3. Has transferred ownership since 1 October 2009.
  4. Has been made available for rent or hire since 1 October 2009.

However, outside of legislative requirements, you will find that it is best to have a mix of both hardwired and battery powered smoke alarms. Hardwired alarms are connected to the mains power and will not work in a power cut.

What is the best placement of smoke alarms?

Smoke alarms should ideally be spread out through the house to cover as much space as possible. Place them in large open spaces to maximise their effectiveness, and avoid putting them over sources of vapour or steam (such as a dishwasher) as this will set off constant false alarms.

All smoke alarms should be mounted on the ceiling. This is because the hot air produced by flaming fires rises, bringing the smoke particles with it. This means that lower placed smoke alarms will not detect fires as well or as soon.

Frequently Asked Questions

Regardless of whether it’s battery or mains-powered, smoke alarms need to be replaced by a licensed electrician every ten years.

You should test your smoke alarms monthly, by holding down the test button until you hear a sound.

You should also dust your smoke alarms regularly, as electronics work best when clear of dust particles. This goes double for fire detection, as working smoke alarms are vital to alerting your home’s occupants. vacuuming around the alarm is the best way to do this without risking damaging the alarm.

The Department of Fire and Emergency Services has a detailed page on smoke alarms. However, the only way to get personalised advice is to speak to your local electrician.

electrical installations

Replacing and installing smoke alarms

Like all electrical installations, you should always have a qualified residential electrician carry out the installation and replacement of hardwired smoke alarms. Prime Time Electricians are not only capable of doing so, but they can also advise you on the best placement of the alarms to best protect your home and family. It is always better to be safe than sorry, especially with a smoke alarm installation or repair.

So if you need your smoke alarms maintained, or just want to have a talk about fire and electrical safety, give Prime Time a call on 1300 356 200 today. 

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