Run a portable generator outside only, at least 20 feet from your house, with the exhaust pointed away from it. Never run one inside your home, garage, basement, crawlspace or shed, even with the doors and windows open. That's the U.S. Consumer Product Safety Commission's rule, and it's the one to follow every single time.

The CPSC warns that carbon monoxide from a generator can kill in minutes. More than 100 people in the U.S. die each year from carbon monoxide linked to portable generators, the agency says. You can't see it or smell it, and people can pass out before they feel the milder signs like nausea, dizziness or weakness.

Where the generator goes

• Outside, at least 20 feet from the house.
• With the exhaust pointed away from your home and any other building someone could walk into.
• With the windows and other openings in the path of the exhaust closed.
• On a dry surface. If it's wet out, run it under an open, canopy-like cover to keep it dry.
• Never on a porch or in a carport. The CPSC says both are too close to the house.
• Never in the garage, even with the big door rolled up.

Before you start it

1. Pick the spot now, in daylight. Walk at least 20 feet out from the house, clear of doors, windows and vents, and check that the exhaust will point away from your home and your neighbor's.
2. Check your CO alarms. The CPSC says to use battery-operated CO alarms, or plug-in alarms with a battery backup, on each level and outside sleeping areas. Test them monthly. Interconnected alarms are best, because when one sounds, they all sound. A plug-in alarm with no battery goes dark in an outage, right along with the lights.
3. Get the right cords. Use heavy-duty extension cords made for outdoor use.
4. Never plug the generator into a wall outlet to power the house wiring.
5. Refuel it cold. Turn the generator off and let it cool down before you add fuel.
6. If you're buying one, the CPSC suggests asking for a model that shuts off automatically when carbon monoxide levels get high.

Other carbon monoxide traps when the power's out

A dark, cold house tempts people into other risky moves. Skip all of these:

• Heating the house with a gas stove or oven.
• Using a camp stove or charcoal grill inside. The Red Cross says to keep them outdoors, at least 20 feet from windows, and the CPSC says never to grill with charcoal in the garage, even with the door open.
• Leaving a car running in the garage, even with the door open.

Our guide to what causes carbon monoxide in a house covers the furnace, water heater and fireplace too.

Know the symptoms

The CPSC lists headache, dizziness, weakness, nausea, vomiting, sleepiness and confusion. If you feel sick, dizzy or weak while the generator is running, get to fresh air right away. Don't wait to see if it passes.

Some people get sick from carbon monoxide faster. The CDC names infants, older adults and people with chronic heart disease, anemia or breathing problems, and says people who are asleep can die before they have any symptoms. If an older parent is running a generator at their house, walk through this list with them.

If a CO alarm sounds or anyone has symptoms, get everyone outside, then call 911. Stay out until responders say it's safe. For questions about a possible exposure, Poison Help is free at 1-800-222-1222, any time of day. Here's the full list of carbon monoxide poisoning symptoms.

Where the Hero Dual Threat Detector fits

The Hero Dual Threat Detector plugs into the wall and has no battery, so it checks the air only when that outlet has power. During the outage itself, your battery CO alarms do the watching. Put those in first.

The detector covers the rest of the year, in the places generators and engines live. Plug one into the garage, one by the furnace and one in the kitchen. It checks the air for carbon monoxide, and for natural gas, methane and propane leaks that a standard CO alarm doesn't pick up. A live readout shows both levels, and an alarm sounds if either one rises, then a faster, urgent one at higher levels.

Set up the battery alarms before storm season. Then get the Hero Dual Threat Detector for the garage and the furnace room.