backup
Carbon monoxide: the alarm has to work when the power does not
CPSC wants generators 20 feet out, exhaust away, never in the garage. Ready.gov wants CO alarms with battery backup on every level. HomeGuide puts a CO detector at $120 to $360 installed. The generator is optional. The alarm that still runs in the dark is not.
Backup power is an engine that burns fuel, or a furnace that still needs air, or a neighbor’s generator pointed at your window. Carbon monoxide is the part of that job you cannot see. CPSC calls it the invisible killer because it has no color and no smell.
This is not a diagnosis page. If a CO alarm sounds, get everyone outside to fresh air and call 911. CPSC lists headache, dizziness, weakness, nausea, vomiting, sleepiness, and confusion as the symptoms people miss because they look like the flu.
Generator placement is where the machine sits. Dual-fuel portable generators is the gasoline sticker vs propane watts. This page is the alarm and the 20-foot rule, because a transfer switch does not make exhaust safe.
Twenty feet, not the garage
CPSC: never run a portable generator inside a home, garage, basement, crawlspace, or shed, even with the door open. Use it outside only, at least 20 feet from the house, exhaust facing away. One portable generator makes as much carbon monoxide as hundreds of cars. They put more than 200 U.S. deaths a year on accidental non-fire CO from consumer products, and more than 100 of those on portable generators.
Ready.gov says the same outdoor rule: generators, camp stoves, and charcoal grills outdoors and at least 20 feet from windows. Do not use a gas stove or oven to heat the house. Let the generator cool before you refuel. Keep it dry.
CPSC: generators and engine-driven tools
A standby on a pad is not a free pass. Placement is NFPA 37 fire clearances plus the lot line. Five feet from an opening is a fire picture on some standby sheets. It is not CPSC’s 20-foot portable rule, and it is not a CO guarantee. Exhaust that washes a bedroom window is still exhaust.
Look for a portable that shuts off when it sees high CO. CPSC points at PGMA G300-2018 and UL 2201. Those labels are about killing the engine, not about putting it in the garage.
Alarms on every level, with a battery
CPSC wants battery-operated CO alarms, or hardwired alarms with battery backup, on every level and outside sleeping areas. Interconnected is better: when one sounds, they all sound.
NFPA’s home page matches that map: a central location outside each sleeping area, every level, and anywhere the local code adds. Test monthly. Replace on the manufacturer’s schedule. Choose a unit with a recognized testing-lab label. If the alarm sounds, move to fresh air first, then call for help from outside.
Ready.gov wants those detectors in central locations on every level, with battery backup, because the outage is when people drag the generator closer to the house.
A hardwired alarm with a dead backup battery is a wall decoration the night the grid dies. Plug-in units that die with the outlet have the same problem unless they have a battery. Buy the backup, then test it.
HomeGuide’s 2026 smoke-detector guide prices a carbon monoxide detector at $120 to $360 installed per unit. Combination smoke-and-CO hardware is $40 to $100-plus before labor, or $140 to $360-plus installed. Labor to hang a detector is $100 to $260-plus. An electrician is $50 to $130 an hour. A sealed 10-year battery unit skips the annual 9-volt ritual.
HomeGuide: smoke detector installation cost
Three levels plus a basement is four boxes, not one over the kitchen. Interconnect is a second conversation: wireless talk or a traveler in the cable. A single plug-in in a junk drawer is not that map.
Two kits, same house
Kit A, battery units you hang this afternoon. CPSC’s battery-operated alarm on every level and outside sleeping rooms. Four boxes on a two-story with basement. HomeGuide’s hardware line for combo units is $40 to $100-plus each before labor. You skip the electrician if you can reach the ceiling. You still replace them on the date on the back. Test monthly. This is the outage kit, because it does not care that the grid is down.
Kit B, hardwired with battery backup. HomeGuide $120 to $360 installed per CO unit, labor $100 to $260-plus. Interconnected so the basement furnace trip wakes the second floor. The backup battery is the non-negotiable part. A 120-volt-only head is dark in the storm that made you roll the generator out.
If Kit A is $200 in parts and Kit B is $1,200 for four heads, you can do A tonight and still budget B. You cannot skip A because the electrician is booked in January.
Alarms you can hear from the pillow, including strobes and bed shakers, are a different page still queued under Aging. Stay here on placement and backup power.
What usually blows the CO job
The generator on the porch “just for tonight.” CPSC’s garage rule includes the porch and the open door. Twenty feet, exhaust away, or you do not run it.
An oven used as a heater. Ready.gov says that in so many words. It is a CO source and a fire.
A standby five feet from a bedroom window because the gas meter was convenient. Placement is a separate bid. Pushing the pad can add trench. Leaving it in the alcove can add a funeral.
Alarms with no battery backup. The storm is when the furnace inducer, the generator, and the space heater all run. The 120-volt-only detector is dark.
One alarm in the hallway, none downstairs. NFPA wants every level. CO from a basement furnace or a garage does not wait at the stairs.
Never replacing the unit. Follow the date on the back. A ten-year sealed battery is still a ten-year clock.
A CO-shutoff generator treated as an indoor machine. UL 2201 is a shutoff. It is not a room-rated heater.
Other fuel, same gas
NFPA’s CO page is not only generators. A car warming up in an attached garage, even with the door up, still dumps exhaust toward the house. After snow, dryer, furnace, stove, and fireplace vents have to be clear or the same gas comes back inside. Charcoal and gas grills belong outdoors, full stop.
Ready.gov’s oven-as-heater line sits next to that list. The outage is when people improvise. The alarm with battery backup is how you find out before morning.
A standby bid should still show the pad, the openings, and who hangs or tests the house CO alarms. HomeGuide’s typical standby is $6,000 to $11,000 installed. That number does not include four new detectors. Add them.
HomeGuide: whole house generator cost
What the driveway questions sound like
Where will the portable sit, measured to the nearest window, door, and garage opening, with the exhaust pointed away?
Does every level already have a CO alarm with battery backup, including outside the bedrooms?
Are those alarms interconnected, and when were they last replaced?
If we are hanging a standby, where is the pad relative to operable openings, not just the gas meter?
Does the portable have CO shutoff listed to PGMA G300 or UL 2201?
Who installs hardwired units, and is HomeGuide’s $120 to $360 per box in this number?
How do I decide this week?
Put working CO alarms with battery backup on every level and outside sleeping rooms before you buy a generator. CPSC and NFPA are the map. HomeGuide’s installed CO box is $120 to $360.
Keep any portable 20 feet out, exhaust away, never in the garage. That is CPSC and Ready.gov, not a brand brochure.
Treat the oven, the charcoal grill, and the running car in the attached garage as the same class of problem. Outside only.
If the alarm sounds, leave, then call 911 from fresh air. Do not open the windows and go back to bed.
Size the machine after the air is safe. Fridge, sump, furnace is the load list. Transfer switch cost is how power gets in without a cord in a dryer outlet. Carbon monoxide is the line you do not negotiate to save a few feet of extension cord.