Mate I'm its even worse than we could possibly imagine by now. ~20 years ago, when smartphones were new and super expensive, I arranged to meet my friend using Facebook chat. I did not have a mobile phone at all, I used desktop PC to access it. While I was in his car we were talking about possible careers and I said i would probably enjoy being a teacher. When I got home and logged back in, every single banner ad was for teaching courses, teach English abroad, teachers wanted. It definitely used his smartphones microphone to hear that there were 2 people in the car, and used the chat log to figure out it was me, and this was a long time ago.