Photoelectric smoke alarm

A photoelectric smoke alarm uses a light-scatter detection chamber: a steady light beam inside the alarm is interrupted when smoke particles enter and scatter light onto a photo sensor, triggering the alarm. Compared to ionisation alarms (which use a small radioactive source to detect changes in air ionisation), photoelectric alarms respond faster to slow, smouldering fires, the failure mode that kills most residential occupants (smouldering bedding, soft furnishings, electrical insulation). Both sensor types fall under AS 3786:2014, the Australian Standard for residential smoke alarms (verified 2026-05-13, Standards Australia).

NCC 2022 Housing Provisions Part 9.5 requires AS 3786 alarms in Class 1 and Class 2 dwellings: mains-powered, interconnected, located in every storey containing bedrooms and the corridor or hallway serving them. NCC does not specify a sensor type (verified 2026-05-13, ABCB NCC 2022 Part 9.5). Queensland’s Fire Services Act 1990 (renamed from Fire and Emergency Services Act 1990 on 1 July 2024) overrides this with stricter rules: photoelectric type only, one alarm in every bedroom and every hallway serving a bedroom, interconnected across all storeys. The retrofit deadline for all existing Queensland dwellings is 1 January 2027 (verified 2026-05-13, Queensland Fire Department).

On a Queensland job, install photoelectric units even where a certifier signs off against NCC alone, state law trumps the deemed-to-satisfy path and an NCC-compliant install can still fail state inspection. Outside Queensland, photoelectric remains the right default for residential bedrooms: the dominant fatal ignition pattern is slow-smoulder, not flaming combustion, and ionisation alarms are slowest to detect exactly that.

Also known as: photoelectric alarm, optical smoke alarm, light-scatter smoke alarm.

Category: Fire safety / electrical / NCC compliance.

Related

See also

Related articles