Interesting read, this one involves Alexa, but I am pretty sure Google an others might be doing the same. A summary:
"Now that you know that your voice recordings are being sent via the internet to a centralized location, you may have assumed Amazon will need to store that data for some period of time — for example, to use its Natural Language Processing algorithms to interpret your request for a weather report (or to buy a pizza), gather that information, and then send it back to your device for it to speak the response."
"Your Alexa-enabled device sends those recordings to an Amazon data center, where they not only use natural language processing algorithms to decode your speech and complete your request, but they also store those files in a centralized database for future use."
"To put it in even simpler terms, if you own an Amazon Alexa-enabled device, Jeff Bezos could be the least creepy person listening to you right now."
I guess the same was said with emails, web browsing, etc, but the fact that the device is "listening" and recording even when you don't call it is a little bit disturbing.
link
https://medium.com/swlh/alexa-play-some-music-isnt-the-only-time-amazon-is-listening-to-you-a556df19613f