SEATTLE — It was the middle of the night, and I heard an alarm that sounded unfamiliar. 

I soon realized the piercing sound wasn't the smoke alarm, but the carbon monoxide detector. A few minutes later, I found the source: My car idling in the attached garage. 

Fortunately the alarm detected the poisonous gas before I or my kids showed any symptoms. 

Last year, the Seattle Fire Department responded to 441 calls related to carbon monoxide. Nationally, 439 people die every year due to carbon monoxide. Charcoal grills are the biggest producers of the gas, and people sometimes put them in the garage during power outages so they can cook. 

"Generators and charcoal grills should be kept outside the house, not even in a carport because carbon monoxide can accumulate quickly," said William Mace, a fire educator for SFD. 

Another big mistake, according to Mace, is people buying the detector but forgetting to install or forgetting to change the battery.