When a Carbon Monoxide Alarm Needs Replacing

Next steps (at a glance)

If you only do 3 things:

  1. Check the manufacture date on each carbon monoxide (CO) alarm.

  2. Replace any unit that is 7–10 years old (check the label).

  3. Test alarms monthly and replace batteries as needed.

Urgency level: Medium
(Becomes High if alarms fail tests, trigger unexpectedly, or you feel symptoms like headaches or dizziness.)

Short answer

Most carbon monoxide alarms need replacement after 7–10 years, depending on the model. Sensors degrade over time and become unreliable, even if the alarm still powers on.

A CO alarm that turns on is not the same as one that can still detect carbon monoxide accurately.

What a carbon monoxide alarm does (and why it matters)

Carbon monoxide is a colorless, odorless gas produced by fuel-burning appliances like furnaces, water heaters, fireplaces, and gas stoves.

CO alarms detect rising levels and alert occupants before exposure becomes dangerous. Because you can’t smell or see carbon monoxide, alarms are the primary warning system.

Typical carbon monoxide alarm lifespan (what most homes see)

  • Carbon monoxide alarms: usually 7–10 years
    Replacement clues: failed tests, frequent false alarms, expired date on label

  • Batteries: replace as needed
    Replacement clues: chirping, weak test sound

Some combination smoke/CO units follow the shorter of the two lifespans.

What shortens carbon monoxide alarm effectiveness

  • Sensor aging

  • Exposure to humidity or extreme temperatures

  • Dust or debris buildup

  • Power surges (hard-wired units)

  • Long periods without testing

CO sensors naturally lose sensitivity over time, even in normal conditions.

Warning signs a CO alarm needs attention

  • Repeated chirping unrelated to batteries

  • Failure during test button checks

  • False alarms with no clear cause

  • Unit past its replacement date

  • Alarms triggering when appliances start up

Any alarm that fails a test should be addressed immediately.

What happens if CO alarms aren’t replaced

  • Delayed or missed alerts during CO buildup

  • Increased exposure risk during appliance malfunctions

  • False sense of safety

  • Higher risk during sleeping hours

Outdated CO alarms often look fine but may respond too slowly—or not at all.

DIY-safe checks you can do

These steps are safe for homeowners:

  • Press the test button monthly

  • Replace batteries when chirping occurs

  • Check the manufacture or replacement date on the unit

  • Gently vacuum vents to remove dust

Do not attempt to recalibrate or open sealed units.

Maintenance that actually helps

  • Monthly testing confirms the alarm still sounds

  • Battery replacement prevents nuisance alerts

  • Unit replacement at expiration ensures reliable detection

  • Dust removal helps keep sensors clear

Testing confirms sound, not sensor accuracy—age still matters.

If you don’t want to call a professional yet but want to stay safe

Prioritize these:

  • Replace expired CO alarms immediately

  • Install fresh batteries when chirping occurs

  • Ensure alarms are installed near sleeping areas and fuel-burning appliances

If alarms trigger repeatedly without explanation, replacement is safer than troubleshooting.

Common mistakes

  • Assuming CO alarms last as long as smoke detectors

  • Ignoring the expiration date

  • Removing batteries to silence chirping

  • Keeping old units because they “haven’t gone off yet”

CO alarms are time-limited safety devices.

When to call a professional

Seek professional help if:

  • CO alarms activate repeatedly without obvious cause

  • Multiple alarms trigger at once

  • You suspect appliance malfunction or venting issues

What to ask:

  • Whether appliance inspection is needed

  • If venting or combustion air issues are possible

What to expect:
Evaluation focuses on appliances and ventilation. Costs vary by home and system type.

Related guides

Disclaimer:
This is general information only. When in doubt, hire a licensed professional.