MaintainlyHow often should you replace your CO detector unit?
Replace CO detector unit every 5 years. The commonly recommended range is every 5 years, or the date on the unit. CO sensors wear out; follow the date on the unit, and the CDC says to replace at least every 5 years if none is given. This is a safety-critical task, so do not let it slip.
A CO alarm does not last indefinitely. The US Consumer Product Safety Commission says alarms have a recommended replacement age, found in the product literature or from the manufacturer, and the CDC’s advice is to replace a detector following the manufacturer’s instructions or every 5 years.
Why does replacing your CO detector unit matter?
CO sensors wear out; follow the date on the unit, and the CDC says to replace at least every 5 years if none is given.
What happens if you skip replacing your CO detector unit?
An alarm past its date gives false reassurance. It can still light up and still respond to the test button, and you have no way to tell at home whether it would still detect carbon monoxide.
How do you do it?
- Find the replace-by date. Printed on the back or the side. If there is no date, treat the unit as overdue and replace it now.
- Buy to the current standard. Check the unit carries the standard or certification mark used in your country, listed in the regional notes below.
- Consider a sealed long-life unit. These remove the battery task and the ambiguity about age, since the unit simply expires as a whole. England’s guidance for landlords prefers sealed for life batteries.
- Place it properly. Follow the manufacturer’s instructions. Keep it out of the kitchen, away from directly above a fuel-burning appliance, away from heating vents, and clear of furniture and curtains.
- Write the install date on it. And record the replace-by date somewhere you will actually see it.
What does it take?
How do you know replacing your CO detector unit is overdue?
- A repeating end-of-life warning that a new battery does not silence
- A replace-by date that has passed
- A unit with no date at all
What do people get wrong?
- Treating the end-of-life warning as a faulty battery and cycling batteries through a dead alarm
- Buying an uncertified alarm online: check for the standard or certification mark rather than the price
- Placing it in the kitchen or directly above a fuel-burning appliance, which the Consumer Product Safety Commission advises against
What changes how often you need to do it?
- Combination smoke and CO units carry one replace-by date for the whole unit, so track it separately from your smoke-only alarms
- After a real CO event, check the manufacturer’s instructions on whether the alarm itself needs replacing
- A CO alarm is a backup to servicing your appliances, not a substitute for it
When should you stop and call someone?
Replacing the alarm is a homeowner job. Working out why one sounded is not: do not use the suspected appliance until a trained, licensed gas or heating technician has serviced it. In the UK the HSE’s first step for suspected CO is the National Gas Emergency Service on 0800 111 999.
Does this differ in the US, UK, Australia or Canada?
United States
The Consumer Product Safety Commission says to choose an alarm that meets the current UL 2034 safety standard. The CDC’s guidance is to replace the detector following the manufacturer’s instructions or every 5 years.
United Kingdom
The government’s guidance for landlords in England recommends alarms that comply with British Standard BS 50291 and prefers sealed for life batteries. That fits the requirement, in force since 1 October 2022, for rented homes with a fixed combustion appliance in a room used as living accommodation. Welsh Government guidance adds that the instructions supplied with the alarm should be followed, including noting its expiry date.
Australia
Follow the replace-by date on the unit. In Victoria the regulator’s emphasis is on servicing gas heaters at least every two years with a licensed gasfitter, so an alarm is the backup rather than the main protection.
Canada
Ontario’s guidance is to replace CO alarms according to the manufacturer’s instructions, and to look for the logo of a recognized testing agency such as CSA, ULC or ETL to confirm the alarm meets Canadian performance standards. Know the difference between the low battery warning, the end-of-life warning and the emergency alarm.
Frequently asked questions
Why does replacing your CO detector unit matter?
CO sensors wear out; follow the date on the unit, and the CDC says to replace at least every 5 years if none is given.
What happens if you skip replacing your CO detector unit?
An alarm past its date gives false reassurance. It can still light up and still respond to the test button, and you have no way to tell at home whether it would still detect carbon monoxide.
Does replacing your CO detector unit differ by country?
Follow the replacement date printed on the unit. The US CDC advises the manufacturer's instructions or every 5 years.
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.
- Fitness of homes for human habitation: guidance for landlords, Welsh Government. Checked 11 October 2026.
- Gas safety: carbon monoxide awareness, Health and Safety Executive. 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.
- Smoke detector installation cost, HomeGuide. Checked 11 October 2026.
Next steps
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