The Independent has previously reported that Google’s voice search function doesn’t just turn on when specifically asked to. It records anything and everything. This has been going on for years, but the public at large became generally aware of it back in the summer of 2015.
Google also carefully keeps track of every single thing you search for on the web… all of it in one nice long history strand that makes a Facebook wall look like peanuts by comparison. Depending on whether or not you have location data on, it can also show you a timeline of where you have physically been, broken out by year on a world map.
Using these three features, Google probably knows more about you than your own mother does.