Carbon monoxide (CO) is a gas you cannot see or smell. The US Consumer Product Safety Commission (CPSC) explains where it comes from and where to put alarms. This is general safety information, so follow the alarm maker's manual too.

This guide is based on the public sources listed at the end. We have not tested the products or services mentioned.

This is a short reference page. The full guide is Home Safety Buying Guide: Heaters, Smoke and CO Alarms, Cords, Candles, Furniture and Smart Devices.

Where CO comes from

Incomplete burning in fuel-burning appliances (furnaces, ranges, water heaters, room heaters, fireplaces), gas-engine equipment (generators, cars, lawn mowers, power washers) and burning charcoal.

Where to put alarms

  • Use battery-operated or battery-backup CO alarms on every level of the home and outside sleeping areas.
  • Interconnected alarms are best, since one sounding sets off all of them.
  • Keep alarms away from fuel-burning appliances, heating vents and spots furniture or drapes could block, and out of kitchens.
  • The CPSC alarms page adds: not in attics or basements unless the space includes a sleeping area. Combination smoke and CO alarms exist.

Testing and replacing

The CPSC says to test alarms monthly and replace the batteries annually. Its fact sheet says to replace the alarm by its recommended age or when the end-of-life signal appears.

If an alarm sounds

Do not search for the source. Get outside, call 911 and do not go back in until responders say it is safe. Early CO poisoning can look like flu without a fever. If you suspect exposure, get to fresh air and see a doctor.

Appliance care

Have fuel-burning appliances and the heating system inspected yearly. Never run a generator or gas engine in or near an enclosed space, and never leave a car running in an attached garage.

Buying

The CPSC pages we read do not name a standard. Check the maker's stated replacement age and whether the alarm can be interconnected. See also portable space heaters.

Last checked: 15 October 2026. Sources: US CPSC, carbon monoxide fact sheet; US CPSC, CO alarms.