I just replaced all of my smoke detectors about a month ago, take a good look at yours, they have expiration dates on them.
We had a guy not show up for work one morning, not like him at all, no call no show. The boss called his house, no answer, he called the police. All the cars in the drive, no answer at the door, they forced entry and found them all unconscious, something wrong with the furnace allowed co2 to build up. Lucky the call was made they all recovered.