Home safety devices have multiplied over the years, and the terminology can blur together. Smoke alarms, heat alarms, and carbon monoxide detectors are all commonly found in New Zealand homes — but they detect different things, respond to different threats, and are suited to different locations. Getting these distinctions wrong can mean the wrong protection in the wrong room.

What a Smoke Alarm Detects

A smoke alarm detects airborne particles produced by combustion. In a photoelectric smoke alarm — which is the recommended type for residential use in New Zealand — a beam of light is directed across a sensing chamber. When smoke particles enter the chamber, they scatter the light beam onto a sensor, triggering the alarm.

Photoelectric smoke alarms respond most effectively to slow, smouldering fires — the type that produces dense smoke before an open flame is established. This is the most common type of residential fire in New Zealand.

Smoke alarms are appropriate for bedrooms, hallways, living rooms, stairwells, and any habitable room where early detection of airborne particles is needed.

What a Heat Alarm Detects

A heat alarm does not detect smoke or combustion particles. It detects temperature — either when the ambient temperature reaches a fixed threshold (typically 58°C), when the temperature rises rapidly, or both. It will not respond to cooking fumes, steam, or dust.

This makes heat alarms the right choice for kitchens and garages, where smoke alarms would trigger from everyday activities. Heat alarms are slower to respond than smoke alarms because they rely on a fire generating significant heat before activating. They should never replace smoke alarms in sleeping areas or escape routes.

What a Carbon Monoxide Detector Does

Carbon monoxide (CO) is a colourless, odourless gas produced by incomplete combustion. It can be generated by gas heaters, wood burners, poorly maintained flues, and vehicle engines. Unlike smoke or heat, it poses a poisoning risk rather than a fire risk — it's possible to be overcome by carbon monoxide in a home with no visible fire and no smoke.

A carbon monoxide detector continuously monitors the concentration of CO in the air and sounds an alarm when levels reach a dangerous threshold. It provides no protection against fire and is not a substitute for a smoke alarm.

Homes with gas appliances, open fires, wood burners, or attached garages are the primary candidates for CO detection. The detector should be placed in bedrooms or sleeping areas — this is where CO poisoning is most dangerous because occupants may be asleep and unaware.

Can Combination Devices Do Everything?

Multi-function devices that combine smoke detection and carbon monoxide detection are available. These can be convenient in homes where both are needed. The key consideration is whether each function meets the relevant standard — the smoke detection component should comply with NZS 4514 and use photoelectric technology, and the CO detection component should meet its own applicable standard.

Combination smoke and heat detectors are also available, designed for open-plan kitchen and living areas. These require careful review to ensure the detection thresholds are appropriate for the specific environment.

Matching Device to Room

A simple way to think about it: smoke alarms belong in rooms you sleep in and rooms you live in. Heat alarms belong in rooms where cooking or fumes are present. Carbon monoxide detectors belong wherever combustion appliances are used and wherever people sleep in proximity to them.

These three types are complementary, not interchangeable. A home that has all three correctly placed has layered protection against different types of risk.