Well there's this: https://news.ycombinator.com/item?id=14459417
But that's legally plausible as just monitoring phone orientation to improve user experience.
How possible it is to reverse the app looking for syscalls to the microphone api or something?
You should probably discard user initiated audio recording if available but looks doable for someone with the knowledge.
Disclaimer: I know almost nothing about reversing
I would pay good money for a study on this.
Ex: Choose a hundred random subjects and assign them irrelevant, obscure keywords to speak loudly into their phones while the messenger app is open. Report back with resulting ads displayed over the following week.
There have been numerous threads about this: https://hn.algolia.com/?query=facebook%20listening
Yes they are listening!!! there are enough discussion about it in the /r/technology and even here at HN
conservations?
conversations?
There's another possibility:
Your friend searched for it or read articles about it @ office. You two share the same geolocation and IP address @ office. Facebook figured out you might be interested in the same topics as what others in your office are searching for. Facebook shows you potentially related articles @ home.
No audio listening required.
I'd be surprised if Facebook Product Managers haven't been doing the above. This is basic.