CO detectors die quietly. Unlike a smoke alarm, the sensor inside a CO detector chemically degrades over time. When the sensor is past its service life, the unit may still chirp on a test button press (testing the battery and speaker, not the sensor) but it can't detect carbon monoxide. Most current models are 10-year units. Older models (pre-2013 Kidde, many older First Alert) are 7-year units. Either way, the date that matters is on the back of the unit.

Quick schedule

  • Every 7 to 10 years: replace the whole unit. Check the "replace by" date on the back.
  • Monthly: press the test button on every CO detector in the house.
  • Yearly: replace user-replaceable batteries (some units have sealed 10-year batteries that match the unit lifespan; nothing to replace).
  • When you hear an end-of-life chirp pattern: replace immediately. The unit can't detect CO once it signals end of life.
  • When digital units show "End" or "Err": replace immediately.

How to find the date on a CO detector

Three ways:

  1. Take the unit off the wall or ceiling. Look at the back. Most have a "manufactured" date and/or a "replace by" date printed on a sticker.
  2. If the unit doesn't have a date sticker or it's faded, the unit is likely old enough to replace.
  3. For digital models, the front display may show a self-diagnostic status.

If you can't find a date and don't know when the unit was installed, replace it. The cost of a new CO detector is $20 to $50. The cost of a CO detector that can't detect anymore is your family's safety.

Why this is different from smoke alarms

Smoke alarms last 10 years (per NFPA). CO detectors last 7 to 10 years, model-specific. They're related but not the same:

  • Smoke alarms have an ionization or photoelectric sensor (or both in dual sensors) that has a 10-year service life regardless of how often the alarm has gone off.
  • CO detectors have an electrochemical sensor that degrades through normal operation. Service life is 5 to 10 years depending on the manufacturer and model.
  • Combination units (smoke + CO) generally have the shorter of the two life spans, which is the CO life.

For more on the difference, see CO detector vs smoke alarm.

What the end-of-life chirp sounds like

Each manufacturer is slightly different. Common patterns:

  • Kidde: a quick beep every 30 seconds, often with a red LED flash. Different from the standard low-battery chirp.
  • First Alert: chirps every 30 seconds with a particular flash pattern. Some models say "Replace alarm" verbally.
  • Digital models: "End" message, "Err" message, or end-of-life icon.

If you're not sure whether it's a low-battery chirp or an end-of-life chirp, replace the batteries first. If chirping continues, it's end-of-life and the unit needs replacement.

Where to put CO detectors

Code in most US jurisdictions for homes with fuel-burning appliances or attached garages:

  • Outside every separate sleeping area (so the alarm wakes sleeping people).
  • On every level of the home, including the basement.
  • At least 15 feet from cooking appliances to reduce false alarms.
  • Not in the immediate proximity of bathrooms where steam can affect sensors.
  • Not in unconditioned spaces (garages, attics) unless specifically rated for them.

Check local building code for placement specifics. Many states have specific requirements.

Common mistakes

  • Replacing the battery and assuming the unit is "new" again. Battery replacement does nothing for sensor wear.
  • Hush-buttoning a CO alarm without leaving the house. CO is invisible and odorless. Trust the alarm.
  • Disabling a chirping alarm because the noise is annoying. The chirp means battery or sensor needs attention.
  • Buying a single $30 unit for a 3-story home. Code is on every level plus outside sleeping areas.
  • Forgetting CO when the focus is on fire safety. CO kills ~400 people a year in the US per CDC.

If the alarm sounds

This is the part that matters more than any maintenance schedule:

  1. Get everyone out of the house. Don't stop to find pets or take things; get out.
  2. Call 911 from outside the house.
  3. Don't go back in until the fire department or gas utility says it's safe.
  4. If anyone has symptoms (headache, dizziness, nausea, confusion), get medical attention.

Don't open windows and "air out" the house instead of calling. CO concentrations can rebuild fast, and the source needs to be identified.

Good maintenance rhythm

  • Monthly: press the test button on every CO detector.
  • Yearly: replace batteries (user-replaceable models) when clocks change in fall.
  • Every 7 to 10 years: replace each CO detector per the manufacturer's date.
  • When moving into a new home: check the dates on every CO detector. Replace any without a clear date or past their life.
  • After any HVAC, fireplace, or fuel-appliance work: test detectors and verify they're still operational.
  • If a CO alarm sounds: leave, call 911, don't go back in until cleared.
Add reminders to the HomeSaver mobile app to always stay ahead of your home maintenance.

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