Always treat a sounding smoke, heat or carbon monoxide alarm as genuine until the cause is confirmed
Check the household, move to safety where required and follow the alarm manufacturer’s emergency instructions. Do not remove batteries or disable alarms simply to stop the noise.
MOST LIKELY CAUSES
Start with the alarm pattern and initiating unit
Symptom variations Match the exact sound, LED and interlink behaviour. ⌄
- Repeating groups of loud beeps
- Single periodic chirp
- Fault or end-of-life LED
- Alarm near boiler, fire or cooker
- Occupants have headache, dizziness or nausea
Safe first checks Checks before reset, cleaning or replacement. ⌄
- Check for smoke, heat, fire or possible carbon monoxide first.
- Identify which alarm is initiating or chirping.
- Record the sound pattern and LED colour.
- Check the manufacture and replacement date.
- Do not disable the household alarm system without providing alternative protection.
Step 1 — Treat a possible CO alarm as urgent Confirm the alarm pattern and household safety before attempting reset or replacement. ⌄
Move people into fresh air, avoid using combustion appliances and follow the alarm manufacturer's emergency instructions.
Step 2 — Call emergency or gas-safety services where appropriate Confirm the alarm pattern and household safety before attempting reset or replacement. ⌄
Do not re-enter or reuse appliances until the situation has been assessed.
Step 3 — Only then identify the warning pattern Confirm the alarm pattern and household safety before attempting reset or replacement. ⌄
Check whether the unit indicates CO, low battery, fault or end of life.
What the warning usually means How this domestic alarm condition develops. ⌄
A carbon monoxide alarm may sound for detected CO, low battery, fault or end of life. Never assume the sound is only a battery warning until the pattern and safety situation are confirmed.
Further diagnostic checks Checks after household safety has been confirmed. ⌄
- Check the exact sound and LED code from the model instructions.
- Confirm alarm age and replacement date.
- Test or replace the battery only after the area is safe.
- Arrange inspection of fuel-burning appliances and flues.
- Replace any alarm reporting end of life or persistent fault.
Information and equipment needed Useful items for accurate checking. ⌄
- Alarm make and model
- Manufacture and replace-by date
- User instructions and sound-code table
- Specified replacement battery where applicable
- Compatible replacement alarm and test method
Parts that may be involved Components commonly associated with this problem. ⌄
- Replacement CO alarm
- Specified battery
- Compatible mounting plate
- Appliance service and flue inspection
- Manufacturer instructions
When immediate action is required Conditions that require urgent response. ⌄
- There may be smoke, fire or overheating.
- A carbon monoxide alarm pattern is sounding.
- Anyone has headache, dizziness, nausea or confusion.
- Multiple alarms have lost mains or interlink operation.
- The only alarm protecting an area has failed.
- The alarm cannot be restored to normal reliable operation.
Frequently asked questions Common domestic alarm questions. ⌄
Can a chirping alarm just be removed?
No. The warning should be identified and the battery or complete alarm replaced while maintaining protection.
Why do all alarms sound when only one detects something?
That is the purpose of interlinking. One initiating alarm warns the entire household.
How do I know which alarm started it?
The initiating unit usually shows a different LED or stored alarm-memory pattern described in its instructions.