Choose the right detector types, place them correctly, test and maintain them on schedule, and know exactly how to respond when each type of alarm sounds.
Having a working smoke alarm reduces the chance of dying in a reported home fire by 54%. CO alarms prevent thousands of carbon monoxide poisoning deaths and hospitalisations each year. These two devices are among the highest-value safety investments any household can make — and they cost less than a restaurant meal.
Yet roughly 40% of home fire deaths occur in homes that have smoke alarms — because the alarms were not working. Dead batteries, units past their service life, alarms placed in the wrong location, or alarms disabled because of nuisance triggers are the common failure modes. This guide covers choosing the right devices, placing them correctly, maintaining them, and understanding what to do when they activate.
Two main technologies detect smoke. Each has different strengths.
Combine both ionisation and photoelectric technology in a single unit. These provide the broadest detection coverage and are the recommended choice for bedrooms and living areas.
Not the same as smoke detectors. Heat detectors trigger when temperature rises above a set threshold or rises rapidly. Used in kitchens, garages, and loft spaces where cooking or dust would cause nuisance alarms from smoke detectors. They do not replace smoke detectors — they detect heat, not smoke or CO, and will only trigger after a significant fire has developed.
All domestic CO detectors use electrochemical sensors — they detect CO concentrations and trigger at specific threshold levels over time periods defined by UL 2034 and EN 50291 standards. The alarm is time-weighted: brief exposure to slightly elevated CO levels or sustained exposure to moderate levels will trigger the alarm.
Some units also detect other gases (VOCs, combustible gases) — these are combination units that add detection capability. A CO alarm and a natural gas/LPG detector are different products. Confirm what your unit actually detects.
Combination smoke and CO alarms in a single unit are widely available and practical for areas where both types of detection are needed (most living areas and bedrooms). These units sound different tones or voice alerts for each type of detected hazard, allowing you to identify which hazard is present and respond correctly.
| Location | Requirement |
|---|---|
| Every bedroom | Inside the room, on the ceiling or high on a wall |
| Outside each sleeping area | In the corridor providing access to bedrooms |
| Every level of the home | Including basement and attic if used for habitation |
| Kitchen | At least 3 metres from cooking appliances (use heat detector in the kitchen if smoke detector triggers too often) |
| Living room | On the ceiling, central if possible |
| Stairwell | Top of stair on the ceiling |
| Garage | Heat detector rather than smoke detector (vehicle exhaust causes nuisance alarms) |
Height rules:
CO mixes evenly with air — it does not rise or sink significantly. Breathing-height placement (1–1.5 metres from the floor) is recommended by most manufacturers.
| Location | Guidance |
|---|---|
| Every level of the home | Required in most modern building codes |
| Outside each sleeping area | Critical — CO alarms must wake sleeping occupants |
| Near fuel-burning appliances | 1.5+ metres away (to avoid nuisance from start-up emissions) |
| Not in bathrooms | Humidity can affect sensor accuracy |
| Not in direct sunlight | Temperature extremes affect performance |
Interconnected alarms — where triggering one sounds all of them simultaneously — provide critical additional warning time, particularly in large homes or when the fire starts far from sleeping areas.
Interconnection is available via:
⚠️ A standalone alarm that sounds only where the fire starts gives someone sleeping two floors away far less warning time than an interconnected system. If your alarms are not interconnected, consider upgrading.
| Task | Frequency |
|---|---|
| Test alarm button | Monthly |
| Clean unit (gentle vacuum or compressed air to vents) | Every 6 months |
| Replace standard 9V batteries | Annually |
| Replace 10-year sealed battery unit | At 10 years (some units give end-of-life chirps) |
| Replace hardwired unit (with battery backup) | Every 10 years |
| Replace entire unit (sensor lifespan) | Every 10 years for smoke; every 5–7 years for CO |
Check the manufacture date printed on the back of every alarm in your home right now. If it is more than 10 years old for smoke or 7 years old for CO, replace it regardless of how well it tests.
Ionisation chambers become contaminated with dust. Photoelectric chambers can accumulate grime on the LED and sensor. CO electrochemical sensors have a finite number of reaction cycles and lose sensitivity over time. A detector that beeps when you press the test button confirms only that the electronics and battery work — it does not confirm the sensor still detects at the required sensitivity level.
The most dangerous alarm is one that has been removed or disabled because it kept going off during cooking. Solutions:
⚠️ Never remove a battery and fail to replace it. The "temporary" disabled detector accounts for a significant proportion of fire deaths in homes where alarms were present.
| Item | Smoke Detector | CO Detector |
|---|---|---|
| Best placement | Ceiling, every room | 1–1.5 m high, every level |
| Technology | Ionisation / Photoelectric / Dual | Electrochemical |
| Test frequency | Monthly | Monthly |
| Sensor lifespan | 10 years | 5–7 years |
| Battery (standard) | Annual replacement | Annual replacement |
| Response | Evacuate; call fire services | Evacuate; call emergency services; medical check |
| Kitchen | Use heat detector or relocate 3 m+ | 1.5 m from appliances |
This guide provides general guidance on detector selection, placement, and maintenance. Requirements vary by country and region. Consult local building codes and fire regulations for applicable standards. Professional installation is recommended for hardwired systems.
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