Generator Carbon Monoxide Safety

The four rules, and the reasoning behind each

1. Outdoors, with no exceptions for part-enclosed spaces

The failure mode people fall into is thinking in terms of degrees of enclosure: a garage with the door up feels halfway to outside. It is not. An open garage door does not produce enough air exchange to clear a generator's exhaust, and the concentration builds in the space regardless. The same applies to a carport, a covered porch, a shed with the doors open, and a basement with a window open.

2. At least 20 feet, exhaust pointed away

Distance is the mechanism that actually protects you, and the direction the exhaust faces matters as much as the distance. CO from a generator five feet from an open window will find the window. Twenty feet, with the exhaust aimed away from the building, is the published guidance.

This has a practical purchasing consequence that catches people out: you need a cord long enough to achieve it. A 10-foot cord cannot put a generator 20 feet away. A 25-foot cord is the realistic minimum and a 50-foot cord gives you genuine freedom about siting. See generator extension cords.

3. Battery CO alarms indoors, on every sleeping level

This is the single most important sentence on this page. A plug-in carbon monoxide alarm does not work during a power outage — which is the exact event during which you are running a generator. If your only CO alarm is hardwired or plug-in without battery backup, you have no CO detection at precisely the moment you most need it.

A battery-powered CO alarm costs around twenty dollars. Buy one before you buy a generator, and buy one per sleeping level. Look for an electrochemical sensor, which is the accurate type for CO, and note that CO sensors have a finite service life — commonly 7 to 10 years — after which the unit needs replacing, not just new batteries.

The short answer

Battery CO alarms — buy before the generator

#	Product	Best for	Score	Price
1	Kidde KN-COPP-B-LPM Battery CO Alarm Buy this before you buy the generator. Battery-powered CO detection is the one piece of equipment that addresses the way generators actually kill people.	The one accessory nobody should skip	9.6/10★★★★★	$23.45
2	First Alert CO400 Battery CO Alarm The right second alarm: put the Kidde on the sleeping floor and this one near the room closest to where the generator sits.	A second alarm for upstairs	9.2/10★★★★★	$21.99

#ad Prices as of October 5, 2026; they may have changed since. Scores are our editorial judgment from published specifications, not test results — how we pick. How we are funded.

4. Symptoms mean leave, not investigate

CO poisoning presents as headache, dizziness, weakness, nausea, confusion, blurred vision. The confusion is the dangerous part, because it impairs exactly the judgment needed to recognize what is happening and act. The rule is therefore mechanical: if anyone in the house feels unwell while a generator is running, everyone goes outside into fresh air immediately and you call emergency services from there. You do not go looking for the cause.

What a CO shutdown on the generator does and does not do

Most current generators include some form of CO shutoff — Generac's COsense, Champion's CO Shield, WEN's Watchdog, DuroMax's CO Alert, Honda's CO-MINDER. These are genuinely worth having and we note their presence or absence on every product in our registry.

But understand what they measure: the CO concentration in the generator's own operating area. Champion's description is representative — it shuts the generator off before harmful levels accumulate in the generator's operating area. That protects someone standing next to the machine. It does nothing about the CO accumulating in your bedroom, because the sensor is not in your bedroom.

Running in bad weather, which is when you need it

The tension here is obvious: outages come with storms, generators must stay outdoors, and generators do not like rain. The correct resolution is a purpose-made running cover — a canopy that sheds water away from the electrical components while leaving the exhaust and the air intake completely open.

What is not a resolution: moving it into the garage, under a tarp, into a shed, or under a closed canopy. A cover solves the water problem and changes nothing about the carbon monoxide problem.

Running covers — for water, not for enclosure

Running a generator in real weather

GenTent Universal Open Frame Generator Tent

$159.99·View on Amazon

Cheapest cover with stated dimensions

Porch Shield Running Generator Cover, 36 x 28 x 20 in

$79.99·View on Amazon

These let a generator run in rain and snow while sitting out in the open. Placement rules are unchanged: still 20 feet away, still exhaust pointed away from the house.

More on the weather question: using a generator in rain.