The devices that we use are not literally listening in on our conversations. However, the services we use regularly — Google, Facebook, grocery or airline loyalty programs, etc. — are collecting data about our online behaviors (searches, current location, purchases, website visits, etc.), cross-referencing this with other data that exists about us (age, marital status, mailing address, income, etc.) and drawing conclusions about what we might be interested in purchasing next.
When you notice an ad that relates to an in-person conversation you had recently, it is merely based on data that exists about you, your interests and your behaviors.
– Emily Reeves Dean, Cranford Co.