Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
A carbon monoxide alarm has a sensor with a finite working life, and it can reach the end of that life while still looking perfectly healthy on the wall. This page covers three things: the date of manufacture on the back label, the end-of-life signal that a fresh battery will not silence, and swapping the unit out. It is not about what to do when the alarm is actually going off. If your CO alarm is sounding right now, stop reading and get everyone outside into fresh air, then call 911 from outside. CPSC is explicit that you do not go looking for the source and you do not go back in until the responders say you can.
How long a CO alarm lasts is genuinely disputed, and this page publishes the disagreement instead of picking a winner. CDC says to follow the manufacturer's instructions or replace the detector every five years. Kidde, one of the largest manufacturers, says its own alarms have a proven life of seven to ten years depending on the model, that everything it built from 2013 onwards is a ten-year unit, and that anything older than that is a seven-year unit. CPSC publishes no universal number at all and says the recommended replacement age comes from the product literature or from the manufacturer. Those cannot be averaged into a fourth answer that belongs to nobody. The number that governs your alarm is the one printed on your alarm and in its manual, so this page shows you how to go and find it.
IF THE ALARM GIVES A CONTINUOUS SIGNAL, MOVE ALL PERSONS OUTSIDE IMMEDIATELY.
Then call 911 from outside. Do not look for the source. Carbon monoxide can kill you before you feel the symptoms.
| Item | Note |
|---|---|
| Flashlight optional | The label on the back of the alarm is small. |
| Pen and paper | Use these to record the date of manufacture. |
| Documentation for the alarm | The documentation gives the replacement age and the meaning of each signal. |
| New carbon monoxide alarm material | Only necessary if the alarm is at the end of its life. |
Estimated 1 min
Estimated 5 min to 10 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
DO NOT REMOVE THE MOUNTING PLATE OF AN ALARM THAT HAS WIRES.
The wires behind the plate can give you an electric shock.
INSTALL THE ALARM AGAIN IMMEDIATELY AFTER YOU READ THE LABEL.
The home has no protection from carbon monoxide while the alarm is off the wall.
Estimated 2 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
Source: CO Alarms · tier 1 · accessed 2026-07-29
REPLACE AN ALARM THAT CONTINUES TO GIVE A SHORT SIGNAL.
An alarm at the end of its life does not sense carbon monoxide.
Estimated 6 min to 10 min
Source: CO Alarms · tier 1 · accessed 2026-07-29
Estimated 4 min
Source: CO Alarms · tier 1 · accessed 2026-07-29
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
Stop this procedure if the alarm gives a continuous loud signal. Move all persons outside to fresh air. Call 911 from outside the home. Do not look for the source of the carbon monoxide. Do not go into the home again until the responders permit it.
Speak to a qualified technician if the alarm gives an alarm signal again after the responders permit entry. A qualified technician must examine each appliance that burns gas or oil. The same is necessary for each appliance that burns wood or charcoal. A qualified technician must also examine the chimney and the vents. This page cannot find the source of carbon monoxide and it does not try.
Stop if the alarm has wires. Do not remove the mounting plate. Do not disconnect the wires. A qualified electrician must do all work behind the mounting plate.
There is no single answer and this page refuses to invent one. CDC says to follow the manufacturer's instructions or to replace the detector every five years. Kidde says its own alarms have a proven life of seven to ten years, that everything it made from 2013 is a ten-year unit, and that anything older is a seven-year unit. CPSC gives no universal number and says the recommended replacement age comes from the product literature or from the manufacturer. Averaging five, seven and ten would produce a number that no authority actually stands behind, so read the figure on your own alarm and in its manual.
It is a maintenance signal rather than an alarm, but which one depends on the model. A short repeated chirp usually means low battery first and end of life second, and the way to tell them apart is to fit a fresh battery: if the chirp stops it was the battery, and if it carries on the alarm has reached the end of its life. The interval that means what is set by the manufacturer, not by any standard, so the exact pattern for your unit is in your manual. What matters is that an alarm in end-of-life mode is no longer detecting anything.
Get everyone outside into fresh air immediately and call 911 from outside. CPSC says not to try to find the source of the carbon monoxide, to do a head count once you are out, and not to go back in until the emergency responders give you permission. Carbon monoxide has no smell and no colour, and CDC notes that people who are asleep or impaired can die from it before they ever notice symptoms. Treat a sounding CO alarm as an evacuation, not as a troubleshooting exercise.
No, and this is a common and dangerous mix-up. Carbon monoxide is CO; carbon dioxide is CO2 and is a different gas with different detectors, usually sold for greenhouses, breweries and ventilation monitoring. A CO2 monitor will not warn you about carbon monoxide. A smoke alarm will not either, unless the unit is a combination smoke and CO alarm, which CPSC notes are sold.
No. An alarm with no battery is not protecting anyone, and carbon monoxide is exactly the hazard you cannot detect for yourself. If the noise is a low-battery chirp, fit the battery the manufacturer specifies. If it is an end-of-life signal, the unit needs replacing and no battery will silence it.
CPSC says to install CO alarms on each level of the home and outside sleeping areas, and not to put them in attics or basements unless those contain a sleeping area. CDC gives the same placement near every sleeping area. Beyond that, follow the installation instructions supplied with your alarm, because minimum and maximum distances from appliances vary by model and some units are not meant for every room.
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
Current version 1 · updated 2026-07-29 · next review due 2027-07-29
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.