Google has recognized in its blog "The Keyword", that they listen to some fragments of the conversations that users have with their devices. They indicate that it is a way to improve the devices, and that the audio fragments heard are not associated with any of the user accounts.
The company has indicated that devices only start listening when you interact with them, and that audio fragments heard account for about 0.2% of total conversations. In addition, the user can choose between deactivating conversations to be recorded or to be deleted every 3 or 18 months.
This information was made public after one of Google's language experts violated security and privacy policies by filtering confidential data from Dutch audios.