The most common smoke alarms that will be found in Queensland Homes are either Ionisation Alarms or Photo-electric Alarms.
Ionisation alarms contain radioactive material between two electrically charged plates which ionises and creates a current. When smoke enters the alarm it disrupts this current and activates the alarm. These alarms are designed to detect flaming fire. Ionisation alarms have a radioactive symbol on the label at the back of the alarm.
Photo-electric alarms, also known as optical, aim a light slightly away from a sensor that sits in a sensing chamber. When smoke enters the alarm it disrupts the direction of the light reflecting it onto the sensor and this activates the alarm. Photo-electric alarms are better at detecting fires that begin with a long period of smouldering, which is typical of most house fires.
In Queensland any new smoke alarms that are installed must be photoelectric.