Smart phone microphone (or metadata?) snooping

I occasionally notice reports of people's phones "spying" on their in-person conversations. I have been agnostic about this and have not been concerned, since no one in this household uses smart phones. I did not think about other people's phones.

Recent incidents, however, have got my attention. This has happened twice, so I don't think it's coincidental. It goes like this:

1. Someone visits my home or property. During our conversation, one of us mentions a specific product or service: …

attention conversations don incidents metadata microphone notice people phone phones privacy reports smart smart phones snooping spying