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A single beep and flash every 40 to 60 seconds usually means a low battery. Two or three beeps every 40 to 60 seconds point to a fault or the end of the alarm’s life. Four loud, continuous beeps mean carbon monoxide has been detected: get everyone out and call 0800 111 999.
Carbon monoxide (CO) is invisible and has no smell. It is produced when fuel does not burn properly, and a CO alarm is the only reliable way to detect it. Every beep, chirp or flash is your alarm telling you something, so never ignore it. An alarm in end of life mode can no longer detect CO.
On this page: If your alarm is going off · What the beeps and lights mean · Flashing with no noise · Test button not working · When to replace your alarm · Need help? · FAQs
Four loud, continuous beeps are a serious warning that carbon monoxide may be in your home. Act straight away:
Get medical help straight away. You may not realise you’ve been affected, and going outside into fresh air won’t treat carbon monoxide exposure on its own.
Signs of exposure include headaches, dizziness, nausea and breathlessness. Our guide to the symptoms at different carbon monoxide ppm levels explains more.
The pattern of beeps and flashes tells you what is wrong. The patterns below apply to all FireAngel homeowner CO alarms, and repeat every 40 to 60 seconds depending on the model. Light patterns vary between models, so check your alarm’s manual if you’re not sure what yours is showing.
| What you hear and see | What it means | What to do |
|---|---|---|
| Four loud, continuous beeps | Carbon monoxide detected | Get out, call 0800 111 999 and follow the steps above |
| 1 beep and 1 flash every 40 to 60 seconds | Low battery | Sealed for life battery: replace the whole alarm within 30 days. Replaceable battery: replace the batteries |
| 2 rapid beeps and 2 flashes every 40 to 60 seconds | Possible fault | Replace immediately. Contact Customer Support if the alarm is under warranty |
| 3 rapid beeps and 3 flashes every 40 to 60 seconds | End of life | Replace as soon as possible. The sensor has a fixed lifespan and cannot be reset |
| 1 regular beep every 40 to 60 seconds after an alarm, with a red LED that double flashes or stays on (varies by model) | Alarm memory: CO was detected recently | See CO alarm memory below |
Regular beeps do not mean low level CO exposure. If an alarm is not silenced while it is sounding, it keeps going until the CO level drops below 50 ppm. Digital display models also show symbols on screen, and our CO alarm icon identifier guide explains what each one means.
A single flash every 40 to 60 seconds with no sound is the power LED showing your alarm is working. If your alarm detected carbon monoxide recently, possibly while you were out, its memory function lets you know with one regular beep every 40 to 60 seconds. Depending on the model, the red LED double flashes every 20 seconds or stays on, and the memory lasts from 48 hours to 7 days. Find out more about CO alarm memory and what to do next.
If your carbon monoxide (CO) alarm doesn’t sound when you press the test button, the next steps will depend on how old your alarm is and whether it is still under warranty.
Carbon monoxide alarms don’t last forever. Over time, the sensor can lose its effectiveness, which is why every alarm has a replace by date printed on the back. It’s important to replace your alarm by this date to help ensure it continues to provide reliable protection.
You should also replace your CO alarm if:
If your CO alarm is due for replacement, browse our range of carbon monoxide alarms to find a suitable replacement for your home.
Our UK based Customer Support team is available from 8:30am to 5:30pm, Monday to Friday. We’re closed at weekends and on bank holidays. Contact Customer Support if your alarm is under warranty and the isolation pin has been removed. If it is out of warranty, or showing a fault or end of life pattern, replace it.
One beep and one flash every 40 to 60 seconds is the low battery warning on FireAngel CO alarms. If your alarm has a sealed for life battery, replace the whole alarm within 30 days. If it takes replaceable batteries, just replace the batteries. If the alarm has sounded recently, one regular beep with a red LED that double flashes or stays on can be the memory function telling you CO was detected. Light patterns vary by model, so check your alarm’s manual.
Three rapid beeps and three flashes every 40 to 60 seconds mean the alarm has reached the end of its life. Replace it as soon as possible.
It means your alarm detected carbon monoxide recently, possibly while you were out. It lets you know with one regular beep every 40 to 60 seconds and a red LED that double flashes every 20 seconds or stays on. The memory lasts from 48 hours to 7 days depending on the model.
No. The sensor has a fixed lifespan and cannot be reset, so the alarm must be replaced.
If you suspect a carbon monoxide emergency, get everyone out and call the Gas Emergency number on 0800 111 999. For advice, you can also call the HSE Gas Safety Advice Line on 0800 300 363.
If you can't find what your looking for on our blogs and looking for further guidance and advice, our UK-based Customer Support team are on hand all week from 8:30am until 5:30pm, they can answer any further queries you may have on our products, solutions or services.
