We had a scare today. The alarm went off while DD was napping. We are powerless from the hurricane, so somehow our generator outside must have tripped it. DH and I went over it a million times and we have no idea how. It was far enough from the house, exhaust away, windows, doors shut, etc. I thank god for that alarm, because it saved my family today. Check the batteries, check if it works... it really may just save your life. Im literally still shaking.
Are you sure it was really getting in the house? Most of those alarms are false. My brother is a firefighter and said that every house should have multiple alarms. That way, if one goes off, but the others don't, then it's just the one malfunctioning. They regularly go bad after awhile. My ILs had theirs go off a few years ago. They called the FD, and the house scanned clean. I'm glad your family is safe though!
Re: FYI... CHECK your Carbon Monoxide batteries.
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Micah Leonard