MaintainlyHow often should you replace your CO detector batteries?
Replace CO detector batteries once a year. The commonly recommended range is every 12 months (test monthly). A non-working CO alarm can't warn you of an odorless, deadly gas. This is a safety-critical task, so do not let it slip. It is seasonal work, best done in autumn / fall.
Carbon monoxide is produced by the incomplete burning of fuel: coal, wood, charcoal, oil, kerosene, propane and natural gas, plus engines such as generators and cars. Health Canada says it can only be detected with a carbon monoxide alarm, which is what makes a flat battery in a CO alarm different in character from a flat battery in almost anything else.
Why does replacing your CO detector batteries matter?
A non-working CO alarm can't warn you of an odorless, deadly gas.
What happens if you skip replacing your CO detector batteries?
The US Consumer Product Safety Commission describes the early symptoms of CO poisoning as similar to the flu but without the fever, and says higher exposure brings confusion, loss of coordination and unconsciousness. People mistake the early stage for illness and stay put, so the alarm is the defence that matters.
How do you do it?
- Do it on the same day as the smoke alarms. One annual pass through the house covers both.
- Note the alarm’s replace-by date. CO alarms have a recommended replacement age set by the manufacturer. The date is on the back or the side.
- Fit fresh batteries. Use the type specified. Some units take AAs, some a 9V block.
- Test with the button. Ontario’s guidance is to press the test button monthly, so treat this as one test of twelve rather than the only one.
- Check placement while you are there. Follow the manufacturer’s instructions first. The US Consumer Product Safety Commission does not recommend kitchens or spots directly above fuel-burning appliances, and says to avoid heating vents and anywhere furniture or curtains could cover the alarm.
What does it take?
How do you know replacing your CO detector batteries is overdue?
- A regular single chirp, which is the low battery warning
- An end-of-life signal, which means replace the unit rather than the battery. The manual shows how it differs from the low battery chirp
- No response to the test button
What do people get wrong?
- Confusing the low battery chirp with the end-of-life warning and fitting batteries into an expired alarm forever
- Mounting it directly above the boiler or furnace, or in the kitchen, against the Consumer Product Safety Commission’s advice
- Treating an alarm that sounds as a false alarm. Go outside to fresh air, call the emergency number, and do not go back in until responders say it is safe
- Assuming a smoke alarm also detects CO, which a smoke-only alarm does not
What changes how often you need to do it?
- Homes with any fuel-burning appliance, a fireplace or an attached garage are the ones Ontario’s law targets, and they are the ones that need CO alarms wherever you live
- Sealed long-life units remove the battery task but still expire
- After any appliance installation or flue work, test again
When should you stop and call someone?
If a CO alarm sounds, get everyone outside into fresh air first, then call the emergency number, and do not re-enter until told it is safe. Do not run the suspected appliance again until a trained technician has serviced it.
Does this differ in the US, UK, Australia or Canada?
United States
Requirements are set by state and local code. The Consumer Product Safety Commission recommends alarms that meet UL 2034 on every level of the home and outside sleeping areas, and the CDC suggests checking the batteries when the clocks change in spring and fall.
United Kingdom
In England, since 1 October 2022 landlords of private and social rented homes must fit a carbon monoxide alarm in any room used as living accommodation that contains a fixed combustion appliance, excluding gas cookers. Those regulations do not apply to owner-occupiers. In Scotland every home with a carbon-fuelled appliance such as a boiler, open fire or wood burner must have a CO detector in the same room, and in Wales landlords must fit one in any room with a gas, oil or solid fuel burning appliance. England’s guidance suggests head height, about 1 to 3 metres from the potential source.
Australia
Energy Safe Victoria’s core advice is servicing rather than alarms: gas heaters should be serviced by a licensed gasfitter at least every two years, and Victorian rental providers must arrange a gas safety check every two years. Treat a CO alarm as a backup to that servicing, not a replacement for it, and check your own state’s rules.
Canada
Requirements are provincial. In Ontario a house needs a CO alarm if it has a fuel-burning appliance, a fireplace or an attached garage. One must be installed adjacent to each sleeping area and, since 1 January 2026, on every storey. Ontario also says to replace batteries yearly and never to run a vehicle inside a garage, even with the door open.
Frequently asked questions
Why does replacing your CO detector batteries matter?
A non-working CO alarm can't warn you of an odorless, deadly gas.
What happens if you skip replacing your CO detector batteries?
The US Consumer Product Safety Commission describes the early symptoms of CO poisoning as similar to the flu but without the fever, and says higher exposure brings confusion, loss of coordination and unconsciousness. People mistake the early stage for illness and stay put, so the alarm is the defence that matters.
Does replacing your CO detector batteries differ by country?
Universal. UK: required in rented homes in England and in all homes in Scotland where there is a fuel-burning appliance. CA: Ontario requires them in homes with fuel-burning appliances. AU: CO alarms are not universally mandated; Energy Safe Victoria advises servicing gas heaters every 2 years.
When in the year is replacing your CO detector batteries best done?
This is seasonal work. Plan it for autumn / fall, before the weather it protects against arrives.
How we put this together
The figures, intervals and legal points on this page were checked against the sources listed below. The default interval and accepted range are the ones Maintainly uses in its task library. Costs and times are typical ranges and vary by region and by home. Your own manufacturer's instructions come first, and gas, electrical and structural work belongs with a qualified professional. How we research and write.
Sources
- Carbon monoxide questions and answers, US Consumer Product Safety Commission. Checked 11 October 2026.
- About carbon monoxide poisoning, US Centers for Disease Control and Prevention. Checked 11 October 2026.
- Smoke and Carbon Monoxide Alarm (England) Regulations: guidance for landlords and tenants, GOV.UK. Checked 11 October 2026.
- Fire and smoke alarms: the law, Scottish Government. Checked 11 October 2026.
- Fitness of homes for human habitation: guidance for landlords, Welsh Government. Checked 11 October 2026.
- Residential property safety checks, Energy Safe Victoria. Checked 11 October 2026.
- Warm up to winter with a home heating safety check, Energy Safe Victoria. Checked 11 October 2026.
- Carbon monoxide safety, Government of Ontario. Checked 11 October 2026.
- Keep carbon monoxide out of your home, Health Canada. Checked 11 October 2026.
Next steps
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