Photoelectric vs. Ionisation Smoke Alarms

Photoelectric or Ionisation Smoke Alarms?

Smoke alarms use either photoelectric or ionisation sensors to detect smoke. You’ll find some that have both types of sensor (“dual” models). Some claim to be “modified” or “enhanced”. But, despite the marketing, they are all some flavour of those first two technologies.

Ionisation smoke alarms are typically more effective at detecting fast flaming fires, which consume combustible materials rapidly and spread quickly. Photoelectric smoke alarms, on the other hand, are typically more effective at detecting slow smouldering fires, which burn for hours before bursting into flame.

On a test conducted by all tested alarms detected smoke from flaming and smouldering fires. The four ionisation alarms in our test were faster at detecting flaming fires (burning oil and wood) but much slower at detecting smoke from smouldering foam.

The job of a smoke alarm is to alert you to a fire so you can get out safely. A fire that develops in the night, when you are asleep, is likely to be the slow smoulder of a faulty electric blanket, curtains draped over a heater, or the plastic coating of a dodgy extension cable. Ionisation alarms, the slowest to respond to this type of fire, are the worst choice. therefore recommends the purchase of photoelectric smoke alarms. Fire and Emergency New Zealand also recommends photoelectric alarms. The Residential Tenancy Act requires landlords to replace expired smoke alarms with long-life battery photoelectric smoke alarms. We think ionisation alarms should not be sold in New Zealand.

Smoke from a flaming waste paper bin or cooking oil fire is different from that produced by the cooler smouldering of upholstery foam, bedding or the plastic bits of electrical equipment. The difference between flaming and smouldering fires is important.

Extracts of content taken from

Note: All smoke alarms sold by PSL Fire & Safety are Photoelectric 1 year or 10 year smoke alarms. View our range here


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