Much of this data [from Android] is collected even when a phone is off-line, then uploaded to Google’s servers and integrated into an archive that includes your search, Gmail, and Google Docs history. The Android platform finds information in your apps and your online activity, and often makes this information available to third parties, like advertisers. A user agreement also gives Google Assistant the right to record conversations that occur within earshot of the device’s microphone.
From Brian Barth’s New Yorker profile of Roger McNamee