How Long Do Carbon Monoxide Detectors Last?

Why a CO alarm has a shelf life

Most home carbon monoxide alarms use an electrochemical sensor: a small cell that produces a tiny electrical current when carbon monoxide reaches it. The chemistry inside that cell slowly changes over time, whether or not the alarm ever detects anything. After enough years, the sensor responds less reliably, and the manufacturer can no longer stand behind its readings.

That is why CO alarms carry a rated life rather than lasting until they break. Smoke alarms work on a different principle and have their own replacement schedule. Combination smoke and CO units follow whichever limit the maker sets for the combined device, which is printed on it.

Finding the date on your alarm

Take the alarm off its mounting plate and turn it over. Most units show a manufacture date, and many also print a replace-by date or a line saying how many years after manufacture the unit should be replaced. Some newer models announce their own end of life with a distinct chirp pattern or a message on a display. If the label has worn off, the model number on the back will lead you to the manual, which states the rated life.

Write the replace-by date somewhere you will see it, such as on the inside of a utility closet door or in your phone calendar. In a house with alarms on several floors, units are often installed at different times, so each one can be on its own schedule.

• Check the back of each unit for a manufacture or replace-by date
• Note whether it is battery-only, plug-in with battery backup, or hardwired
• Look for a sealed long-life battery, which ties the battery to the unit's life
• Keep the manual, or note the model number for looking it up later

Chirps, beeps and what each one means

A CO alarm has several sounds, and they mean very different things. The full alarm is a loud, repeating pattern that does not stop on its own. A short single chirp every minute or so usually signals a low battery. Many units also have a separate end-of-life signal, often a different chirp pattern, sometimes paired with a flashing light or a word on the display. Some have a fault signal as well.

The patterns are not the same across brands, so the manual for your model is where to decode them. New Jersey's Division of Fire Safety advises that if a trouble signal sounds, check for a low battery and replace it, and if the signal continues, call the fire department. A unit that keeps chirping after a fresh battery, or one with a sealed battery that starts chirping, may be telling you it has reached the end of its life.

Testing is not the same as checking age

Pressing the test button confirms that the horn, the circuit and the battery work. On most models it does not expose the sensor to carbon monoxide, so a passing test on an old alarm says nothing about whether the sensor has drifted. That is the main reason age matters even when everything seems fine.

Test anyway. New Jersey's fire-safety guidance says to test CO alarms at least once a month and to replace them according to the manufacturer's instructions. A monthly test catches dead batteries, disconnected hardwired units and alarms that were painted over or taken down during renovation and never put back.

Battery, plug-in and hardwired units

How an alarm is powered changes how it ages in practice. A unit with replaceable batteries needs a fresh battery on the schedule its maker gives, and its sensor still wears out on its own clock. A unit with a sealed long-life battery is designed so the battery and the sensor reach the end together, which is why the whole alarm is replaced rather than opened.

Plug-in alarms with battery backup lose protection during a power cut if the backup battery is dead. Hardwired alarms draw house power but still carry a backup battery in most cases and still have a rated life. None of these power options extends the life of the sensor itself.

Local rules in New York City and New Jersey

In New York City, a 2016 local law on smoke, carbon monoxide and gas detecting devices refers to replacing these devices when they reach the end of their useful life and ties that useful life to the manufacturer's suggestion. It also divides duties between owners and occupants, including maintenance of battery-operated devices inside an apartment. NYC's housing agency summarizes that owners must install at least one approved, working smoke and carbon monoxide detector in each apartment, while tenants maintain them, including testing and replacing batteries.

New Jersey sets its own carbon monoxide alarm requirements, and they differ by type of building and by situation. Rules change, so confirm the current requirements with your city or town before relying on any summary, including this one. This is general information, not legal advice.

Where the alarms should be

The EPA, citing the Consumer Product Safety Commission, says every home should have carbon monoxide alarms on each level and outside each sleeping area. Follow the manufacturer's instructions for mounting height and distance from fuel-burning appliances, because placing an alarm right beside a boiler or in a steamy bathroom can cause nuisance alarms or damage.

Older homes in this region often have the boiler and water heater in a basement, venting into a masonry chimney that also runs past bedrooms on upper floors. An alarm in the basement near those appliances, plus alarms on each sleeping level, covers the places where trouble starts and the places where people are asleep when it happens.

Replacing alarms and fixing the source

When you replace an alarm, use one listed for the purpose, follow its instructions, and do not reuse an old mounting plate if the new model uses a different one. Hardwired alarms in a multi-family building or a renovated house may be interconnected so one triggers the others; matching that system is a job for an electrician if you are unsure.

An alarm only warns you. The CPSC, as quoted by the EPA, also urges a yearly professional inspection of fuel-burning appliances, including furnaces, water heaters, fireplaces and stoves. A blocked chimney, a collapsed liner or a disconnected flue pipe is how carbon monoxide reaches living space in many homes, and our inspection checks every flue the appliances vent into, with a free written estimate if something needs repair.