Why this page exists
Portable generators produce carbon monoxide in quantities that kill, and the U.S. Consumer Product Safety Commission publishes fatality statistics on it every year because people keep misjudging the risk.
The three recurring mistakes are the same every season: running the machine in a garage with the door open, running it under a deck or a window, and assuming that because it is technically outdoors it is far enough away. It generally is not.
CO has no color, no smell and no taste. Early symptoms — headache, dizziness, nausea — read as tiredness, and people go to bed. An alarm is the only thing between you and that.
Placement
The guidance is one alarm on every level of the home, plus outside each sleeping area, tested monthly. Practically, for a two-story house with a basement that means three units.
- Outside every bedroom. The alarm has to wake a sleeping person through a closed door.
- On every level, including the basement. Attached garages and basements are where exhaust accumulates first.
- Not right beside fuel-burning appliances. Normal brief emissions from a furnace or a water heater cause nuisance alarms.
- Not in humid or very cold spaces. Bathrooms and unheated garages are outside most units' rated conditions.
Height is less critical than people assume — CO mixes fairly evenly with air rather than rising or sinking strongly — so follow the manufacturer's instruction for your specific unit rather than a general rule.
Alarms expire, and almost nobody checks
Electrochemical sensors degrade. Every CO alarm carries a manufacture or replacement date printed on the back or side of the housing, and once past it the unit may power up, chirp on test, and still fail to detect carbon monoxide.
Two habits, both free:
- Read the date on the housing now. Not the battery date — the unit's own end-of-life date.
- Test every alarm twice a year, at the same time you exercise the generator. The test button checks the horn and the circuit; it does not verify the sensor, which is why the printed date is the real answer.
What the numbers on the display mean
| Reading | What it indicates |
|---|
| 0 ppm | Normal indoor air |
|---|
| Any sustained reading above 0 | Something is producing CO indoors — investigate before it climbs |
|---|
| Alarm sounding | Get everyone outside into fresh air, then call emergency services. Do not re-enter to investigate |
|---|
Displays on these units begin reporting at 30 ppm; below that they show zero. Alarm thresholds are time-weighted by UL standard — higher concentrations trigger faster. Treat any non-zero reading as information, not as permission to wait.
The rules that make the alarm a backstop rather than the plan
An alarm is the last line, not the first. The generator rules that prevent it ever mattering:
- At least 20 feet from windows, doors and attached garages, per Ready.gov, with the exhaust pointed away from the house.
- Never in a garage, even with the door fully open.
- Never under a deck, an awning or an overhang. Exhaust collects under anything that traps it.
- Never in a shed or under a tarp. A purpose-made running cover is the rain answer.
- Check where the wind is going. A safe position in the morning can be the wrong one by evening.
The full safety guidance covers placement, weather and the specific mistakes that recur.
If you own a battery instead
A power station produces no exhaust of any kind and can sit in a bedroom. That is the strongest safety argument in the category and one of the real reasons batteries have taken share from small generators.
You still want CO alarms — furnaces, water heaters, fireplaces and attached garages all produce CO independently of any generator — but the backup power itself stops being a source. Generator versus power station weighs the rest of the trade.
