We smelled fumes and thought it was the furnace since it had just started. It went away and we could find no cause. It had been inspected and given a thumbs up a few months ago. Decided to replace the smoke detectors (1985 vintage). Got new ones with CO detection. While installing and with mistake that had them bleating for a few minutes the cats went crazy. It seemed to be the voice was more maddening than the bleating. Smart cats I guess.