# My carbon monoxide alarm is going off what do I do? Get everyone outside to fresh air and call 911 from outside. CPSC says do not look for the source, and that opening windows will not provide enough > Source: https://servpronorhfremont.com/questions/fire-emergency-and-structure/my-carbon-monoxide-alarm-is-going-off-what-do-i-do/ > Last reviewed: 2026-08-22 --- Read this before anything else ## Carbon monoxide and smoke inhalation Carbon monoxide is an odorless, colorless gas. CDC lists the most common symptoms of poisoning as headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, and describes them as flu-like. If a CO alarm is sounding, or anyone has these symptoms, get everyone and every pet outside first, then call 911 from outside. Do not go back in. - Home - All questions - Fire emergency and structure - My carbon monoxide alarm is going off what do I do? # My carbon monoxide alarm is going off what do I do? - Fire & smoke Professional required This page explains the work. It does not tell you how to do it, because doing it without training and equipment is unsafe. Get everyone outside to fresh air immediately, including pets, and call 911 or your fire department from outside. CPSC says not to look for the source, and that opening doors and windows will not provide enough ventilation to prevent a lethal buildup. Do a head count once you are out. ## The first hour - Get everyone out of the building now — people and pets — and go to fresh air outside. Do not stop to find the source. CPSC is explicit about this. - Call 911 or your fire department from outside , or from a neighbor's home. - Do a head count. Confusion is a symptom of CO poisoning, and someone may not have followed you out. - If anyone has symptoms, say so on the call. Headache, dizziness, weakness, nausea, vomiting, chest pain or confusion. CDC notes these are frequently mistaken for flu. - Do not go back in until the fire department or your utility says the building is clear. - Do not reset the alarm and carry on. An alarm that sounded is reporting a hazard, not malfunctioning. First action Everyone out Open a window? Not enough Call from Outside ## The short version - CPSC — "If the alarm signal sounds do not try to find the source of the CO. Immediately move outside to fresh air." - CPSC — "Call your emergency services, fire department, or 911." - CPSC — opening doors or windows "will not provide enough ventilation to prevent the buildup of lethal levels of CO." - CDC lists the symptoms as headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion. - If anyone has symptoms, leave and report them from a neighbor's home. You could lose consciousness if you stay. ## What CPSC says, in its own words # Link to this section If the alarm signal sounds do not try to find the source of the CO. Immediately move outside to fresh air. Call your emergency services, fire department, or 911. After calling 911, do a head count to check that all persons are accounted for. Never ignore an alarming CO alarm! It is warning you of a potentially deadly hazard. And the instruction that contradicts most people’s instinct: Opening doors or windows will not provide enough ventilation to prevent the buildup of lethal levels of CO. That last one is worth sitting with. The reflex on hearing an alarm is to open something and stay put while you work out what happened. In a building generating carbon monoxide, that is the decision that keeps you in it. ## The symptoms, and why they are missed # Link to this section CDC lists them: The most common symptoms of CO poisoning are headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. CDC also notes they are frequently compared to influenza-like illness. Two features distinguish them in practice. Everyone in the building feels it at once , including pets. And it improves when you leave and returns when you come back. Confusion is on that list, which is the reason CPSC asks for a head count outside. A person affected enough to be confused may not reliably follow everyone else out. If you have symptoms, CPSC’s instruction is to get outside to fresh air immediately and report them to your fire department from a neighbor’s home — because you could lose consciousness if you stay. ## What causes it # Link to this section Any appliance that burns fuel can produce carbon monoxide if combustion is incomplete or the exhaust is not leaving the building: - A furnace with a cracked heat exchanger, or a blocked, disconnected or corroded flue - A water heater back-drafting because the building is under negative pressure - A gas range used for heating, or an unvented space heater - A blocked chimney — nests and debris are a seasonal cause - A generator, pressure washer or vehicle running in a garage, even with the door open - A charcoal or gas grill used indoors or in a garage Storm season and the first cold week of the year are when this cluster peaks, and both CPSC and USFA publish warnings on that schedule. ## After the building is cleared # Link to this section The fire department meters the building and tells you when it is safe to enter. That is not the same as the fault being fixed. Before anything is used again, the appliance needs a licensed heating technician or the utility, and the alarm that sounded should be checked for age — CO alarms have a service life and expire. There is also a property question hiding behind the safety one. An appliance burning incompletely often deposits residue as well as gas. A furnace puff-back spreads fuel-oil soot — oily, acidic, and carried by the duct system into rooms nowhere near the appliance. If surfaces near supply registers have a fine oily film, or the house smells of oil, that is a separate loss and it is worth documenting while the cause is fresh. ## Why this needs a professional Carbon monoxide is colorless and odorless, so nobody can find the source by looking, and the search itself is the dangerous part — it keeps you inside a building with a concentration high enough to have triggered an alarm. That is why CPSC's instruction is to leave first and not to investigate. Finding it requires a combustion analyzer and a working knowledge of appliance venting: a cracked heat exchanger, a blocked or disconnected flue, a back-drafting water heater, an unvented space heater, a generator or a vehicle in an attached garage, or a chimney obstructed by a nest. The fire department will meter the building; a licensed heating technician or your utility will find and correct the appliance fault. Neither task is one to attempt while the alarm is sounding. ## What this means for your claim A carbon monoxide incident is usually a health and safety event before it is a property claim , and often there is no property damage at all. Where a claim does arise it is normally the appliance failure behind it — a cracked heat exchanger, a failed flue — and whether that reaches a policy depends on whether it is treated as a sudden failure or as wear. If the same combustion failure also produced soot, that is a separate and clearer property loss. A furnace puff-back deposits fuel-oil soot through the ductwork and across the building, and it is generally a covered sudden event. Keep the fire department's report and the heating technician's findings — those two documents establish what happened and when. ## What comes next An appliance producing carbon monoxide is burning incompletely, and the same failure often deposits fuel-oil soot through the ducts — the residue type from a furnace puff-back. If there is a fine oily film on surfaces near registers, that is a property loss on top of the safety incident. See smoke residue types and the first hour . ## Common mistakes - Looking for the source before leaving. CPSC says to leave and not to investigate. - Opening windows and staying inside. CPSC states that is not enough ventilation to prevent lethal levels. - Calling from inside the house. Make the call from outside or from a neighbor. - Treating symptoms as flu. CDC notes CO poisoning is frequently mistaken for influenza-like illness. - Resetting the alarm and going back to bed. The alarm did its job; the hazard has not changed. ## Common follow-up questions ### What if the alarm stops on its own? Treat it as having sounded. Concentrations move around a building as doors open and appliances cycle, and an alarm that silences itself has not established that the hazard is gone. CPSC's instruction to never ignore an alarming CO alarm does not come with an exception for one that stopped. ### Could it be a false alarm? It could, and that is not something to determine from inside the building. CO alarms do expire and do fail, and the way to establish which happened is to leave, let the fire department meter the building, and then check the alarm's date. The cost of being wrong in the other direction is not recoverable. ### How do I know if it is CO poisoning or flu? This site does not diagnose anyone and cannot. Two patterns are worth telling a clinician or the 911 dispatcher about — everyone in the building, pets included, feeling unwell at the same time, and symptoms that ease when you go outside and return when you come back in. CDC notes the presentation is frequently mistaken for influenza. ## Related questions - The first hour after any loss - Smoke residue types and why they differ - What to photograph and log ## Sources Every source cited on this page - T1 Carbon Monoxide Fact Sheet — US CPSC (accessed 2026-08-25) - T1 About Carbon Monoxide Poisoning — CDC (accessed 2026-08-25) - T1 CO Alarms — US CPSC (accessed 2026-08-25) Written by: PLACEHOLDER — Restoration Reviewer Reviewed by: PLACEHOLDER — Claims Reviewer Safety reviewed by: PLACEHOLDER — Restoration Reviewer Last reviewed: 2026-08-22 Guidance that does not name a water category, a smoke type, or the peril and whether the water was internal or external is not specific enough to act on. This page names them.