The source article, posted on Protocol, is titled "Google's secret home security superpower: Your smart speaker with its always-on mics" with the subtitle Google speakers are listening to more than just voice commands. Using them for home security could supercharge Google's $450 million ADT deal.
So the gist is that the device is listening not only for voice commands, but for other ambient noises as well.
This has been reversed, according to a statement from Google, as reported in The Independent.
From the Independent article:
Although the feature provides greater security it is a trade off for less privacy. Google has adamantly pushed that the only way its smart speaker will listen to users is via its wake word.
The use of ambient monitoring for other reasons could lead to questions about what else Google will request to monitor in the future especially since all that stands in the way of a users acquiescence is a privacy policy that few will ever read.
Google is not the only company with this feature; Amazons Echo speakers added a feature like this in 2018 called Alexa Guard.
I realize many (most?) people who buy a smart speaker don't give a crap what it listens to (or even records), but it creeps me out. Which is why I don't have one.
https://scienceline.org/2018/04/smart-speaker-records-often-think/