Apparently, they don't actually do this. However, they do do the next best thing:<p>1) You talk to a friend, in-person or by message, about [topic]<p>2) You go about your business<p>3) Your friend Googles [topic]<p>4) Google associates [topic] with your friend's ad ID, as well as the ad IDs of anyone they've been near in the past 24 hours (you)<p>5) You and your friend see ads about [topic]<p>I don't know how smart they are about it, but it's likely working on the same system that runs their location services "Your reviews/photos are being read on Google, answer questions about [place you recently visited]?", and Google Rewards which tracks your location to ask you about receipt data and other things. It's very good at knowing if you've been into a lcoation and spent time there.<p>So, if they know a group of people were at a location for a period of time together, and those people have done so before, they can show ads based on one group member's search history to all of them.<p>No creepy message reading, or sneaky microphone recording, just regular creepy location tracking.