Why does my smoke alarm go off when I cook?

Smoke alarms respond to particles in the air, and frying, grilling and toasting produce exactly those particles in quantity. So does steam, which scatters light in an optical chamber just as smoke does. An alarm that goes off twice a week is not faulty — it is being asked to do a job it was never designed for, in a room full of the thing it detects. The reason this matters so much is behavioural: the household that is woken by false alarms is the household that takes the battery out.

Safety

What you'll need

• A heat alarm for the kitchen
• An optical (photoelectric) smoke alarm for the hall (optional)
• A vacuum cleaner with a soft brush
• A stepladder
• A screwdriver and wall plugs (optional)

Step by step

1. Check what type of alarm is in or near the kitchen.The label on the back says. A smoke alarm in a kitchen is the wrong device — kitchens need a heat alarm, which triggers on a rapid temperature rise rather than on particles.
2. Fit a heat alarm in the kitchen and move the smoke alarm out.Heat alarm on the kitchen ceiling, centrally. The nearest smoke alarm goes in the hall, at least three metres from the cooker and clear of the doorway the steam comes through.
3. Choose an optical smoke alarm for anywhere near a kitchen.Optical (photoelectric) alarms are much less prone to nuisance triggering from cooking than the older ionisation type, and they are better at detecting the slow smouldering fires that actually kill people at night.
4. Keep it 300mm clear of walls, corners and light fittings.Air stagnates in the corner between wall and ceiling, so an alarm too close to a wall responds late to real smoke and erratically to everything else. The same clearance applies around downlights and pendant fittings.
5. Run the extractor from the start of cooking, not when it smokes.An extractor at full speed from before the pan goes on removes fumes as they are produced. Started afterwards it just moves the cloud around. Check the filters — a greased-up filter halves the airflow.
6. Shut the kitchen door while cooking.It keeps fumes out of the hall where the smoke alarm is, and a closed kitchen door at night is one of the most effective fire safety habits in a home.
7. Vacuum the alarm every few months.Dust and insects in the chamber cause false alarms and delayed real ones. A soft brush attachment around the vents, with the alarm still on the ceiling, takes 30 seconds.
8. Use the hush button rather than the battery.Almost every modern alarm has one; it silences for around ten minutes and rearms itself. That is the correct response to burnt toast, and it is why a hush button is worth paying for.
9. Check the age on the back and replace at ten years.Sensors degrade. A ten-year-old alarm becomes both less reliable at detecting fire and more prone to false alarms, whatever the battery says. There is a date on the back of every one.
10. Interlink them once you are fitting new ones anyway.Interlinked alarms all sound when one detects. It is the difference between hearing an alarm through a closed bedroom door at 3am and not hearing it at all. Radio-interlinked battery models need no wiring.

Tips

• Grilling and high-temperature frying are the worst offenders, and steam from a kettle or a pan of pasta accounts for many of the rest. If the alarm goes off when nothing is browning, it is steam and the answer is ventilation.
• In Scotland every home must have interlinked smoke alarms in the living room and every circulation space on each storey, a heat alarm in the kitchen, and a CO alarm where there is a fuel-burning appliance. It is a useful standard to aim at anywhere in the UK.
• Do not paint an alarm, and never use aerosol furniture polish or air freshener near one — the residue coats the sensing chamber.
• A steam-prone bathroom doorway needs the same treatment as a kitchen: move the alarm, do not remove it.

Common mistakes

• Taking the battery out until after dinner — It is the single most common reason a smoke alarm fails to save a life, because nobody remembers to put it back. Use the hush button, or fix the placement.
• Fitting a smoke alarm in a kitchen because 'that is where fires start' — Fires do start there, which is exactly why the kitchen needs a heat alarm that will not be disabled. A smoke alarm in a kitchen gets removed within a month.
• Mounting the alarm in the corner or right beside a light — Corners are dead air, and heat from a light fitting drives a rising air current past the sensor. Both cause late detection and erratic false alarms.

If it doesn't work

Questions people ask