Losing power during the cold weather can be more than an inconvenience; it could spell carbon monoxide danger.

Dr. Tom Waters of the Cleveland Clinic says carbon monoxide is known as the silent killer because it’s colorless and odorless. He says carbon monoxide is most likely a risk in the winter when furnaces are running. It’s important to have furnaces serviced at least once a year.

It’s also essential to have carbon monoxide detectors in your home. If your house doesn’t already have them wired into ceilings and walls, there are detectors that can plug right into a wall outlet. Waters says it’s best to check both smoke and carbon monoxide detectors twice a year. It’s also important to know the signs of carbon monoxide poisoning.

“If you notice in a loved one, or someone else, or a friend that they’re experiencing symptoms such as headache, nausea, excessive daytime sleepiness, fatigue, lethargy…those are all signs that they might be being exposed to carbon monoxide and you want to have that checked,” Waters said.

If you lose power during the winter, Waters says you should never use a gas oven to supplement your heat. If you use a generator, you should make sure it’s in a well-ventilated area.