Carbon monoxide gives no warning a person can rely on. It has no smell, and the early symptoms look like flu without the fever. On 4 July 2026, two children aged 8 and 12 were found in a garage in Sumpter Township, Michigan, next to a portable generator their family was running after storms cut the power; fire officials said at least three people had died of carbon monoxide in south-east Michigan that weekend (ClickOnDetroit, 6 July 2026).
That is the pattern the research keeps finding. This page is the practical companion to our analysis, It Looks Exactly Like Flu, Except for the Fever.
Every step carries a label for how strong the evidence is: Measured outcome data exists; Official advice a public body recommends it but its effect is rarely measured; Untested sensible, but we found no study. Hover or tap a label for the definition.
Before: an alarm, a service, and one rule about engines
When an ice storm cut power to most of Mecklenburg County, North Carolina, in December 2002, 124 people were poisoned in nine days. Investigators found that 96.2% of the severe cases were in homes with no working CO alarm (CDC, MMWR 2004).
- A CO alarm on every level, and outside every sleeping area. Measured Battery-powered or with battery backup, so it still works when the power is out. Keep it away from heating vents and out of the kitchen; do not mount it above a fuel-burning appliance. CPSC
- Check the date on the alarm. Official advice CO sensors wear out, usually in five to seven years, whether or not they have ever gone off. Replace the whole unit, not just the battery.
- Know that a smoke alarm is not a CO alarm. Official advice Unless the label says it is a combination unit, it will not detect carbon monoxide.
- Have the boiler, furnace or heater serviced every year by a qualified technician. Official advice CPSC
- Never run a generator, a car or a charcoal grill in or near an enclosed space. Measured That includes garages, basements, sheds and covered porches, and it applies with the doors and windows open. Outdoors, keep a generator well away from windows, doors and vents. CPSC
If it happens: recognise it, then leave
The signs that point to carbon monoxide rather than a bug are about the pattern, not any one symptom.
- Suspect CO if several people, or people and pets, feel ill at the same time. Official advice Headache, dizziness, nausea, tiredness and confusion, with no fever. Feeling better away from home and worse again on return is a strong clue. see our analysis
- Get everyone out first. Do not open windows and stay put. Official advice Leaving is the treatment; ventilating while you stay inside is not. CPSC
- Call from outside, then count heads. Official advice Tell the responders if anyone is missing, asleep or unwell. CPSC
- Do not go back in until responders give permission. Official advice Not for the car keys, not to switch the boiler off. CPSC
Afterwards: a doctor, and a technician
- See a doctor, and say you suspect carbon monoxide. Official advice Feeling better in fresh air does not mean nothing happened. Tell them how long you were exposed and who else was there. CPSC
- Do not use the suspected appliance until it has been properly serviced. Official advice CPSC
- Replace an alarm that went off if it is near its expiry date. Untested And add alarms on any level that did not have one.
What not to do
- Do not run a generator in the garage “with the door open”. Measured In a 2005 US survey, 63.3% of adults either agreed that this was safe or were not sure (King & Damon, 2011). It is not.
- Do not take the battery out of a CO alarm that keeps sounding. Official advice Treat the alarm as real until someone with a meter says otherwise.
- Do not heat the home with a gas cooker or a charcoal grill during a power cut. Measured Charcoal grills were a major source of poisoning in winter storms (Iqbal et al., 2012), and gas kitchen ranges were used for heat in many of the homes poisoned after a 2006 snowstorm in New York State (Muscatiello et al., 2010).
Checklist
Do it twice a year, when the clocks change, alongside the smoke alarms.
- CO alarm on every level and outside every sleeping area
- Pressed the test button on each one
- Checked the expiry date printed on each alarm
- Alarms have batteries or battery backup
- Heating serviced in the last twelve months
- Generator kept outdoors, away from windows, doors and vents, with fuel for a power cut
- Everyone in the home knows: alarm sounds, everyone out, call from outside
Where you live
| United States | United Kingdom | Australia | |
|---|---|---|---|
| Emergency | 911 | 999 | 000 (112 from a mobile) |
| Official CO advice | CPSC Carbon Monoxide Information Center | NHS; the Gas Safe Register for gas appliances | Your state energy safety regulator |
How strong is the evidence?
The evidence on where carbon monoxide deaths come from is strong. A review of US disaster-related poisonings from 1991 to 2009 found generators were the main source in 83% of deaths, and two-thirds of those generators were indoors; 89% of the deaths happened within three days of the disaster starting (Iqbal et al., 2012). That is why the generator rule is labelled measured.
The evidence that alarm laws save lives is weaker than you might expect. When New York City required CO alarms in 2004, investigations finding dangerous indoor levels rose nearly sevenfold, so the alarms were clearly detecting more. But the falls in hospital admissions and deaths were not statistically significant, and by 2009 only 54% of residents had recently tested their alarms or changed the batteries (Wheeler-Martin et al., 2015). The authors note that small numbers may have hidden a real effect. An alarm you have tested is the part that matters.
Read next
This guide is general information, not medical advice. Anyone who may have been exposed to carbon monoxide should be assessed by a doctor, even if they feel better.
Sources
- Centers for Disease Control and Prevention. Use of carbon monoxide alarms to prevent poisonings during a power outage — North Carolina, December 2002. MMWR 2004 (reprinted in JAMA). JAMA reprint
- Iqbal S, Clower JH, Hernandez SA, Damon SA, Yip FY. A review of disaster-related carbon monoxide poisoning: surveillance, epidemiology, and opportunities for prevention. American Journal of Public Health 2012. doi:10.2105/AJPH.2012.300674
- Muscatiello NA, Babcock G, Jones RR, et al. Hospital emergency department visits for carbon monoxide poisoning following an October 2006 snowstorm in western New York. 2010. PubMed 20104834
- King ME, Damon SA. Attitudes about carbon monoxide safety in the United States: results from the 2005 and 2006 HealthStyles survey. Public Health Reports 2011. SAGE
- Wheeler-Martin K, Soghoian S, Prosser JM, et al. Impact of mandatory carbon monoxide alarms: an investigation of the effects on detection and poisoning rates in New York City. American Journal of Public Health 2015. doi:10.2105/AJPH.2015.302577
- U.S. Consumer Product Safety Commission. Carbon monoxide questions and answers. Accessed 14 October 2026.
- ClickOnDetroit. Wayne County children die from carbon monoxide poisoning after generator used during power outage. 6 July 2026.
- ROR Labs. It looks exactly like flu, except for the fever (CDC alarm guidance, symptom pattern and mortality figures, with sources).