Reddit user brazedowl shared a screenshot of his Android device showing Google Home notifications responding to the smoke alarm, indicating the device had been snooping around for alarm sounds in the background. Google had accidentally rolled out an update to its Home devices which tested certain home security features, possibly related to an upcoming business deal. Google has since reverted the update, and has in fact mistakenly pushed out this feature on the users’ devices. The new Nest Aware feature gives you the option to call 911 emergency services straight from the Home app.
Source: https://www.bleepingcomputer.com/news/google/google-home-erroneous-update-reveals-the-450-million-adt-deal/