Two alarms, two hazards: planning smoke and carbon-monoxide protection at home

The small boxes on the ceiling and near a boiler are easy to lump together, yet they watch for different hazards. A smoke alarm looks for an early sign of fire; a carbon-monoxide alarm warns about a dangerous concentration of an invisible, odourless toxic gas. Neither replaces the other, and neither replaces professional inspection of combustion appliances, flues and ventilation.

1. Name the hazard first

Install smoke detection where smoke from a developing fire can reach it early. A central hall and the route towards bedrooms are sensible starting points, but one device may be insufficient in a large or multi-storey home. Cooking smoke and steam can cause nuisance alarms in kitchens; the London Fire Brigade recommends a heat alarm there because it reacts to a rapid rise in temperature.

A CO alarm belongs where combustion gases may occur: close to a boiler, fireplace, tiled stove or other fuel-burning appliance. A CO alarm is not a smoke detector, and a smoke detector is not a reliable CO alarm.

2. Read more than the brand name

For smoke alarms, look for reference to EN 14604. For CO alarms, look for EN 50291, the CE mark, the manufacturer and an exact model number. Check the manufacture or expiry date and how the device signals the end of its service life.

Hungary's National Directorate General for Disaster Management still provides earlier laboratory-test lists of CO alarms that passed or failed. They are useful model-level evidence, but the authority's market-surveillance period ended on 30 September 2024. A historic list does not replace checking current packaging, documentation and product recalls.

3. Smoke alarms: high, but not anywhere

The manufacturer's installation drawing comes first. General fire-service guidance places a smoke alarm on the ceiling, near the centre of a room or hallway, at least 30 centimetres from walls and light fittings. Keep it away from kitchen fumes, bathroom steam, doors, windows and supply-air vents. Paint, dust and insects can impair operation, so renovation should be followed by an inspection and careful cleaning.

4. CO alarms: do not plan around the myth that “CO simply rises”

MVM explains that carbon monoxide mixes with room air rather than collecting only at the ceiling. In a room containing a potential source, a general starting distance is 1–3 metres. On a wall, the alarm should sit above the top of doors and windows but at least 15 centimetres below the ceiling; on a ceiling, at least 30 centimetres from walls. Breathing height matters in bedrooms. The specific manufacturer's instructions always take priority over generic dimensions.

Do not hide the alarm behind a curtain, furniture or inside a cupboard, and keep it away from extractor fans, vents, doors and windows. Its sound must wake sleepers through a closed bedroom door.

5. The test button is not decoration

Test smoke alarms with the button at least monthly and vacuum or dust them gently every three months according to the manual. Replace batteries when the device and instructions require it. A sealed ten-year battery does not make the sensor immortal: record the replacement year and replace the entire alarm at the end of its stated service life.

Apply the same monthly routine to the CO alarm, record its expiry date and learn its fault signal. Do not try to “calibrate” it with vehicle exhaust, cigarette smoke or another improvised method. The button checks the alarm's electronics; sensor accuracy requires a proper test process.

6. Design for audibility

Use the test button during the day and from a sleeping position, with doors closed. In a complex or multi-storey home, interlinked alarms can make every unit sound when one detects danger. A resident who is deaf or hard of hearing may need strobes, a vibrating pad or another supplementary alert. The right location must not only detect a hazard; it must wake people in time.

7. Prepare the words and actions for a real alarm

Never dismiss a CO alarm. If it is safe and immediate, open windows and switch off the combustion appliance, then move everyone into fresh air. Confirm that nobody remains inside. Call 112 if anyone feels unwell, if there is a fire or if the situation is uncertain. Do not restart the appliance until it has been inspected by a professional.

For a smoke or heat alarm, getting out comes before investigating the cause. Everyone in the household should know the escape route and meeting point. In a real fire, stay outside and call 112.

8. A five-minute autumn checklist

• Are smoke and, where needed, CO alarms both present?
• Are the model, standard marking and expiry date legible?
• Is every alarm clear of furniture, curtains and dust?
• Can the signal be heard through closed doors?
• Does the test button work, and do you recognise the fault signal?
• Are battery and whole-device replacement dates recorded?
• Does everyone know where to go and whom to call?

Good protection is not a flashy smart-home feature. It is a layered system: the correct device, the correct position, routine testing, maintained building services and a rehearsed response.