Types of smoke alarms
Mains powered alarms
DFES recommends every home should have mains powered smoke alarms. A mains powered smoke alarm is one which is wired direct to a 240 volt AC power supply or to a 12/24 volt DC system powered by a 240 volt supply.
It is important to note that all mains powered smoke alarms must be installed by a registered electrician, and must comply with Australian Standard 3786 and carry the Australian Standards or the ActivFire labels.
Interconnectable smoke alarms can be set up in a network where if one smoke alarm is activated, all other smoke alarms on the same network will also activate.
This can be very useful in larger homes where it may be difficult to hear smoke alarms that are at the other end of the house or on another level.
Some more advanced networks can have isolator buttons included. Once you are made aware of the alarm, pressing the isolator button will switch off all the alarms except for the one that initially activated the alert.
Ionisation and photo-electric alarms
There are two types of smoke alarms; ionisation and photo-electric. Each alarm detects smoke differently.
Research indicates photo-electric smoke alarms consistently provide sufficient time for occupants to escape from smouldering and flaming fires, provided the alarms are installed and maintained properly and occupants hear them.
Ionisation alarms use a small amount of radioactive material to ionise the air in the sensing chamber. As a result, the air chamber becomes conductive, permitting current to flow between two charged electrodes. When smoke particles enter the chamber, the conductivity of the chamber air decreases. When conductivity is reduced to a predetermined level, the alarm is set off.
Photo-electric smoke alarms consist of a light emitting diode and a light sensitive sensor in the sensing chamber. The presence of suspended smoke particles in the chamber scatters the light beam. This scattered light is detected and sets off the alarm.
DFES recommends photoelectric smoke alarms for use in the family home.