How to Tell Whether Your CO Alarm Is Ready for an Outage

Yes, household carbon-monoxide alarms go bad and eventually require complete replacement. Before an outage, also confirm that alarms are tested monthly, installed on every level and outside each separate sleeping area, and able to operate if utility power fails. The U.S. Consumer Product Safety Commission provides this replacement, testing, placement, and backup-power guidance.

This guide uses CO alarm for the complete household device that detects carbon monoxide and sounds a warning, although people commonly call it a detector.

The quick answer: replace on schedule, at end of life, or when age is unknown

Use this three-part decision rule:

1. Replace on schedule. Check the label and manual for the service life or replace-by instructions for that exact model.
2. Replace at end of life. If the alarm gives the end-of-life signal documented in its manual, replace the complete unit. Installing a new battery does not renew an expired alarm.
3. Replace when age is unknown. If you cannot read the label, identify the model, locate its instructions, or establish its age and replacement schedule, replacement is the prudent choice.

There is no universal replacement age for every CO alarm. Estimates such as “around seven years” or “7–10 years” can prompt an inspection, but they cannot override the label and manual for the alarm in your home.

For a five-minute pre-outage check:

• Locate every CO alarm in the home.
• Photograph the front and back labels.
• Record each model number and every printed date.
• Find the manual for the exact model.
• Mark any alarm that is expired, signaling end of life, missing required backup power, or impossible to identify.
• Save the photographs and manuals somewhere accessible without internet service.

Do this before you expect to operate a portable generator or other fuel-burning equipment. During an outage, an unfamiliar chirp is much harder to investigate if the alarm label is hidden, the manual is unavailable, or your phone has no connection.

Replacement is only one part of the check. An in-date alarm still needs the correct power source, routine testing, proper placement, and a location where occupants can hear it.

How to check an alarm’s age and replacement date

Remove the alarm from its mounting plate only as directed by the manufacturer. Look for:

• The manufacturer and model number
• A manufacture date
• An activation or installation date
• An expiration or replace-by date
• Instructions for interpreting end-of-life signals
• Battery or backup-power requirements

Do not assume that the most visible date is an expiration date. It might identify manufacture, activation, purchase, or another event. Use the manual for the exact model to determine what the date means and how its replacement period is calculated.

First Alert, for example, says the date printed on the back of the alarms covered by its guidance is the manufacture date, not the expiration date. It describes an approximate service life of 7–10 years after first activation under normal operating conditions, while noting that the exact period can vary by model. That guidance is specific to First Alert products and should not be applied automatically to other brands. Check First Alert’s explanation of alarm dates and service life.

The Seattle Fire Department gives around seven years as a general life expectancy for CO alarms. Treat that figure as an inspection prompt, not a universal replacement deadline: an alarm approaching that age should be identified and checked against its own instructions. Seattle Fire Department explains its approximate seven-year guidance.

Printed dates may also be incomplete for your purpose. A manufacture date does not necessarily tell you when an alarm was activated, and a warranty period is not automatically the same as its service life. Record what the label actually says rather than converting one type of date into another without support from the manual.

If the label is unreadable and you cannot establish the model, age, or replacement schedule, replace the alarm. Do not try to assign it a service life based on its appearance or on guidance written for another product.

Use these two compact tables to inventory your alarms without creating an excessively wide spreadsheet:

Location	Level	Model	Manufacture or activation date
Upstairs hallway	Second floor
Near basement stairs	Basement

Location	Manufacturer’s replace-by date	Power source and backup status	Last monthly test
Upstairs hallway
Near basement stairs

Use the same location name in both tables so the records can be matched easily. If the manual gives no simple calendar date, write down its exact replacement instruction rather than estimating one.

Keep the completed inventory with your outage plan. Store label photographs and manuals on a phone or another device that will remain accessible if utility power and internet service fail. A paper copy of the alarm-signal page can also be useful if the model uses several different chirps, display messages, or indicator lights.

Signal-to-action table: emergency alarm, low battery, fault, or end of life

Move immediately to fresh air and call 911 or the fire department from there. Do not delay evacuation to inspect batteries, reset the unit, or search indoors for the source. For a recognized low-battery trouble signal, replace the specified battery; NFPA says to contact the fire department if the trouble signal continues after the low battery is addressed. Review NFPA’s alarm-response guidance.

Signal category	Possible meaning	Immediate action
Active CO warning	Carbon monoxide may be present	Move to fresh air immediately and call 911 or the fire department from outside.
Low-battery trouble signal	A replaceable battery may be low	Follow the manual and install the specified battery. If the trouble signal continues, contact the fire department.
Fault or unfamiliar signal	Power trouble, malfunction, sensor fault, or a possible CO warning	If exposure is possible or the warning cannot be identified safely, evacuate first. Identify the signal using the exact manual from a safe location.
Documented end-of-life warning	The complete alarm has reached its replacement point	Replace the complete alarm. Do not rely on a battery change or temporary silencing feature.

A periodic chirp may indicate a low battery, fault, power problem, or end-of-life condition, depending on the model. An unfamiliar signal should not be dismissed merely because it is intermittent.

Some products provide recognizable end-of-life examples. Kidde says certain digital alarms display “Err” followed by “E09” or display “End” and emit a quick beep every 30 seconds at end of life. These are examples for the Kidde digital alarms covered by that support page, not a decoder for every Kidde product or other manufacturer’s alarm. See Kidde’s model-specific end-of-life examples.

If your alarm’s documented end-of-life signal appears, replace the complete unit even if installing a new battery temporarily changes its behavior. A silencing feature can reduce the noise while replacement is arranged, but it does not extend the alarm’s stated service life.

Test monthly and verify the alarm will work when power fails

Test every CO alarm at least monthly according to its manufacturer’s instructions. For plug-in alarms, confirm that the model has the battery backup needed to continue operating during an outage and install or replace batteries according to the manufacturer’s recommendations. Do not assume that a plug-in unit will remain powered when utility electricity fails. CPSC recommends monthly testing and battery backup for plug-in CO alarms.

Follow that procedure rather than improvising a test.

A successful button test does not override the alarm’s replacement date or a documented end-of-life warning. It also does not establish that an expired alarm has additional service life. If the manual says the unit must be replaced, a passing button test is not a reason to keep it in use.

For hardwired or other mains-powered alarms, consult the exact manual to determine whether the model includes backup power and how the manufacturer directs you to test it. The word hardwired identifies the normal power connection; by itself, it does not establish what the alarm will do after utility power fails.

For each alarm, confirm only what its documentation allows you to confirm:

• The complete unit is still within its stated service life.
• No documented end-of-life warning is present.
• The test procedure produces the result described in the manual.
• Replaceable batteries match the specified type and schedule.
• Any required backup-power arrangement is present.
• The alarm has no unresolved trouble or fault signal.

After testing, update the inventory rather than relying on memory. Record the date of the test, any battery replacement, and any unit replaced. If an alarm later signals during an outage, the saved manual should help distinguish a documented trouble condition from an active warning—but possible CO exposure still takes priority over troubleshooting.

Place alarms on every level and outside sleeping areas

Install working CO alarms on every level of the home and in a central location outside each separate sleeping area. Follow the manufacturer’s instructions for the exact position and mounting height; there is no single mounting height suitable for every alarm. Applicable laws, building codes, rental rules, or standards may require additional alarms or a particular configuration. See NFPA’s placement guidance.

For example, a two-story house with a basement needs coverage on:

• The basement
• The first floor
• The second floor
• The area outside each separate sleeping area

“Every level” and “outside sleeping areas” are separate parts of the baseline. An alarm in an upstairs hallway does not provide the required basement-level coverage. Likewise, a unit on each floor does not necessarily address separate sleeping areas located in different hallways or wings.

Use the alarm’s manual to resolve practical mounting questions. Do not choose a height solely because another alarm in the home is installed there, and do not transfer installation instructions from a different model.

When reviewing coverage, walk through the home rather than counting alarms from memory.

Keep indoor alarm placement separate from outdoor generator placement. “Every level and outside sleeping areas” describes where alarms belong inside the home. The 20-foot generator rule describes where portable equipment must operate outdoors; it is not an alarm-installation distance.

A working alarm does not make a generator or backup heat source safe

Power outages can increase CO risk because households may use engines and fuel-burning equipment for electricity, heat, or cooking. Carbon monoxide can build up in enclosed or partly enclosed spaces, and an alarm is a final warning layer rather than permission to operate equipment in an unsafe location.

Operate a portable generator outdoors only and at least 20 feet from the home and its windows, doors, and vents, following the generator manufacturer’s instructions. Never run one in a home, basement, garage, crawlspace, shed, covered porch, or another enclosed or semi-enclosed location—even with a door open. CDC also advises using a battery-powered or battery-backup CO alarm when operating a generator or other fuel-burning equipment. CDC’s outage guidance explains the 20-foot separation and battery-backed alarm precautions.

A history of running a generator in a garage, shed, or porch without a noticeable problem does not establish that the location is safe. Do not move a generator closer because of rain, theft concerns, extension-cord convenience, or the presence of a working CO alarm. Address those practical problems without violating the required outdoor separation.

Other fuel-burning equipment needs its own instructions. Heating and cooking equipment that burns fuel can produce CO, and a gas oven must never be used to heat the home. Do not apply a generator rule as a substitute for the manual, fuel restrictions, ventilation requirements, clearances, and local fire-safety guidance for a backup heater.

Before an outage:

• Identify every fuel-burning device you might use.
• Find and save the manual for each device.
• Confirm which equipment is intended for the planned location.
• Establish a generator location that meets the outdoor clearance before power is lost.
• Verify that the home’s CO alarms are current, correctly placed, tested, and able to operate without utility power.

If a CO alarm gives an active warning while any fuel-burning equipment is operating, leave for fresh air immediately and call 911 or the fire department from outside. Do not remain inside to shut down equipment or locate the source.

Should carbon-monoxide alarms be interconnected?

Interconnected CO alarms can improve whole-home warning because all connected units sound when one detects CO. That can be particularly useful when the initiating alarm is in a basement, on another floor, or away from an occupied sleeping area.

Check applicable local rules and follow the instructions for the alarms being installed. Interconnection supplements proper coverage; it does not replace the need for working alarms on every level and outside each separate sleeping area.