Electrician Explains How Smoke Detectors Work

Nearly 75% of home fire fatalities happen in homes without smoke detectors or where they are not functional. Installing and maintaining smoke detectors is an effective and inexpensive way to protect you and your loved ones from a potentially deadly fire.

Australian legislation also requires residential buildings to have smoke detectors and a battery backup. If you plan to buy one, this article discusses the types of smoke detectors, how they work, and their pros and cons to help you decide.

What a Smoke Detector Does

Smoke alarms are essential components of your home’s safety equipment. A well-installed and functional smoke detector alerts you of early signs of a fire, giving you time to respond and get to safety.

A slow-smouldering fire can remain undetected for a long time before bursting into high-heat flames. A fast flaming fire only burns briefly before the heat and flames intensify.

Whichever the case, a smoke detector immediately senses the smoke particles and triggers a high-pitch alarm.

The Two Types of Smoke Detectors

There are two categories of smoke detectors based on the detection sensor type: photoelectric and ionisation. Both photoelectric and ionisation detectors are adequate, but their performance level differs in various types of fires.

How a Photoelectric Smoke Detector Works

Photoelectric smoke detectors have a detection chamber with a light-sensitive sensor or photocell and an infrared light beam.

The light projection remains at a 90-degree angle. If there are smoke particles in the chamber, they interfere with the light that reaches the sensor. These changes cause the photocell sensor to trigger an alarm.


  • The absence of radioactive materials makes them safer to use
  • Photoelectric smoke detectors work best in rooms with large furniture such as countertops, beds and couches
  • They react better to smouldering fires


  • Regular maintenance due to sensitivity to insects and dust particles can be expensive.
  • Unlike smouldering fires, they can be less effective in fires with big flames.

How an Ionisation Smoke Detector Works

Ionisation smoke detectors have an ionisation chamber. This chamber contains a small radioactive material like americium between two charged plates.

This arrangement creates a continuous electric current inside the chamber. If smoke particles enter the chamber, they interrupt the current flow, triggering an alarm.


  • Ionisation smoke detectors are faster at detecting fires that spark from combustion, such as lightning strikes
  • The alarm often sounds when there’s less detectable smoke than photoelectric detectors


  • There’s a higher likelihood of false alarms due to their mechanism, so most people intentionally disable them
  • They are less effective when detecting smouldering fires
  • Radioactive materials are a concern
  • Best suited for rooms with highly combustible materials that spread flames faster such as flammable liquids, cleaning products and newspapers


FPA Australia recommends a photoelectric smoke detector in any residential building. However, Ionisation smoke detectors react faster to flaming fires which can be risky in a home.

It’s best to have both types because they complement each other for better protection for you and your loved ones. Plan your smoke detector installation immediately, and remember to schedule regular maintenance to ensure they remain functional.

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