A carbon monoxide alarm on the wall is not the same thing as a working carbon monoxide alarm. Sensors age, batteries die, units reach end of life, and an indicator light proves only that the unit has power — not that it can still detect gas.
This is the maintenance discipline behind the placement guide. Placement decides where the warning comes from; this page decides whether the warning still works. Both support the operating boundaries set in the generator carbon monoxide safety guide.
The intervals
CPSC’s guidance is straightforward: use battery-operated alarms or alarms with battery backup on each level and outside separate sleeping areas, test CO and smoke alarms monthly, and never ignore an alarm. (Source: CPSC, 2026 winter storm and power outage safety warning.)
Build the household routine around four intervals:
| Interval | Task |
|---|---|
| Monthly | Press the test button on every alarm; confirm it is audible from inside each bedroom with the door closed |
| Per manufacturer | Replace batteries on the schedule in the instructions, or immediately on a low-battery chirp |
| Twice a year | Check the manufacture and replacement dates on every unit; vacuum dust from the cover per the manual |
| End of life | Replace the entire unit per the manufacturer’s stated service life — not just the battery |
Anchor the monthly test to something you already do. A household that tests “when we remember” tests once.
The failure people do not see coming: sensor end of life
This is the part that catches careful households. CO sensors have a service life, and it is shorter than the life of the plastic box around them. A unit installed years ago can be powered, lit, and completely unable to detect gas.
CPSC’s own framing is blunt: check the manufacture or replacement date and the instructions printed on each alarm. “The light is on” does not prove the sensor is within service life.
Practical rules:
- Find the date on every alarm today. It is usually printed on the back or side. If you cannot find one, treat the unit as suspect.
- Write the replacement date on the unit in marker when you install it, so the next person does not have to hunt.
- Replace the whole unit at end of life. A fresh battery in an expired alarm is worse than no alarm, because it produces confident silence.
- Do not rely on the chirp to tell you about end of life. Some units signal it, some do not, and the signal patterns differ by model. The manual is the authority.
Decode the chirp before you touch the battery
An intermittent chirp is the alarm communicating. It usually means low battery or end of life — the patterns differ by model, and the manual tells you which.
What matters is what you must not do: never remove the battery and stop there. A silenced alarm is not a solved problem; it is a home with no CO warning and no reminder that it has no CO warning. That is a common step in fatal-event timelines.
A continuous alarm is not a maintenance issue. That is the alarm response guide: everyone out, call 911 from outside, no re-entry until responders clear it.
Test correctly
Pressing the test button verifies the horn and electronics. It does not verify the sensor’s ability to detect carbon monoxide.
That distinction matters:
- The test button is still worth pressing monthly — it catches dead batteries, failed horns, and units that have been quietly disconnected.
- Do not attempt to test the sensor by exposing an alarm to exhaust, smoke, or any combustion source. Never create CO to test a detector.
- The only reliable protection against a degraded sensor is replacement at end of life, which is why the date check carries as much weight as the monthly test.
Also confirm audibility, not just function. An alarm heard in the hallway but not through a closed bedroom door at night is a placement problem — see the placement guide.
Check for recalls
CO alarms are safety devices, and safety devices get recalled. Check the exact model and manufacture date against CPSC recalls, and follow the stated remedy. (Source: CPSC, Recalls.)
Do the same for any fuel-burning appliance and portable heater in the home. A recalled alarm and a recalled heater are the two halves of the same bad night — and the indoor limits for fuel-burning heaters decide which of those appliances should never run inside in the first place.
Renters and landlord-supplied alarms
- Battery replacement per the instructions is usually a resident task.
- Report a dead, expired, missing, or chirping-and-unfixable alarm in writing to the landlord or management, and keep a copy. Written requests create records.
- Do not remove, disable, cover, relocate, or “fix” a hardwired or interconnected alarm. That is qualified-electrician or landlord work.
- Many jurisdictions impose specific requirements on rental housing; local code may be stricter than any general guidance here.
A maintenance log
Keep one record for the household and update it when anything changes.
| Alarm location | Model | Manufacture date | Replace by | Battery changed | Last monthly test | Notes |
|---|---|---|---|---|---|---|
| Outside sleeping area 1 | ||||||
| Outside sleeping area 2 | ||||||
| Each additional level | ||||||
| Near attached garage |
Fold the seasonal checks into the routine you already run — the seasonal energy efficiency checklist and the home inspection calendar are natural places to catch the twice-a-year date check.
Combination and smart alarms do not change the schedule
Combination smoke-and-CO alarms are common and convenient, but they add a trap: the two sensors do not necessarily share a service life, and replacing the unit for one reason does not reset the other. Read the manual for both stated lifetimes and treat the shorter one as the replacement date for the whole unit.
Connected or “smart” alarms add a notification path, not a longer sensor life. An app that reports “all good” is reporting connectivity and power, not sensor accuracy. Treat the phone alert as a convenience layer on top of an audible alarm, never as a replacement for one — a notification is useless to a sleeping household whose phone is charging in another room, and it does nothing for a guest.
Sealed-battery units remove the annual battery task and the temptation to borrow the battery for something else. They do not remove the end-of-life replacement. The date check still applies.
Five mistakes that defeat a good alarm
These are the patterns that turn a correctly bought alarm into no alarm at all:
- Silencing a chirp by removing the battery and never returning to it. The most common one, and the most dangerous.
- Replacing the battery in an expired unit and treating the problem as solved. Fresh power, dead sensor, confident silence.
- Testing only the alarm you walk past. The one outside the far bedroom is the one that has to wake somebody.
- Assuming a hardwired alarm is maintenance-free. It still has a service life and, usually, a backup battery.
- Moving an alarm to stop nuisance activations near a fuel appliance, instead of asking why an appliance near the alarm is producing enough CO to trigger it. That activation may be the warning.
If any of these has happened in your home, the fix is not guilt — it is the date check and the log below, today.
Why this matters more before winter
Heating season is when fuel-burning equipment runs hardest and when households improvise heat during outages. That is the moment an expired alarm becomes a fatal detail rather than a maintenance oversight.
Do the date check in the fall, before the first cold snap and before the first storm — the same pass that schedules furnace service. The fuel-burning heater limits warning explains why the alarm is a warning layer and never a permission slip, and the extreme cold hub holds the plan the alarm is protecting.
The honest limit
A tested, in-date, correctly placed alarm is a good warning device. It is not protection. It does not remove carbon monoxide, does not make unsafe equipment safe, and does not tell you a concentration you can tolerate. It buys you the seconds to leave — which is the entire point, and the whole reason the schedule above is worth keeping.
ReadyLience has not tested any CO alarm and recommends no product. Certification, listing, local code, and the manufacturer’s instructions decide what is appropriate.
Sources reviewed
ReadyLience reviewed current CO alarm and carbon-monoxide information guidance from CPSC, its 2026 winter storm and power outage warning, CPSC recall resources, and U.S. Fire Administration heating-safety guidance. Testing and replacement intervals are cited as published guidance; the exact alarm’s instructions, service life, and local code take precedence. This page states no method for testing a sensor with real carbon monoxide and no safe exposure level. Emergency services determine re-entry, clinicians control medical evaluation, and qualified electricians and fuel-appliance professionals control hardwired-alarm and appliance work. The page remains in expert review.