Carbon monoxide is a colorless, odorless gas that is a byproduct of incomplete combustion, e.g. from a poorly maintained gas heater or furnace. It can also be generated by flameless chemical heaters, charcoal grills, badly vented fireplaces, or ones with blocked flues, and vehicles running their engines in a garage.

If you have a gas furnace, fire or stove you should also install carbon monoxide alarms. Many of them plug into a power outlet near the floor and also act as emergency lights.

The devices, which retail for $20–$60 USD and are widely available, can either be battery-operated or AC powered (with or without a battery backup).

Since carbon monoxide is colorless, tasteless and odorless (unlike smoke from a fire), detection in a home environment is impossible without such a warning device.

The main symptoms of carbon monoxide poisoning include: chest pain; confusion; dizziness; headache; nausea, vomiting and weakness.