These are fair questions! I'm not convinced that it is happening. Nor am I convinced, as the parent seems to be, that it would be difficult to do.

edit: Having re-read my comment, I can see how it could easily be read to say "It's happening and this is how it works", whereas I intended to convey something like "It could easily be done and here's how." I have a bad habit of implying my point rather than stating it outright. I'm working on it!

I have a suspicion it’s not Facebook or Google listening in, but rather other third party apps. In fact it’s not even the third party apps but the libraries/frameworks they use to show ads.

There will be no proof until somebody inside Apple who is in on the scam decides to grow a conscience and blow the whistle. Then they will be dismissed as a "disgruntled employee". Decompiling Siri probably will get you a lot of attention from very expensive lawyers that will make your life very interesting for a long while.

I can't even begin to tell you how many times I've been randomly having a conversation with someone, only to be alerted to the sound of the Google Assistant suddenly responding to what we're saying. Something we said was interpreted as a wake word, and then from that point on, every single thing we said was transcribed via STT, sent to Google's servers, various Google search queries were run, etc, and then the assistant responded - because it thought it was responding to a valid query and had no way of knowing otherwise. This has gotten worse with Gemini but has in no way been limited to that.

In this situation, I was alerted to this because the assistant started responding. However, I've also been in situations where I tried deliberately to talk to the assistant and it failed silently. In those situations, the UI spawns the Assistant interaction dialog, listens to what I say and then just silently closes. Sometimes this happens if there's too much background noise, for instance, and it then just re-evaluates that it wasn't a valid query at all and exits. Sometimes some background process may be frozen. Who knows if this happens before or after sending the data to the server. Sometimes the dialog lingers, waiting for the next input, and sometimes it just shuts off, leaving me (annoyingly) to have to reopen the dialog.

Putting that together, I have no idea how many times the Google Assistant has activated in my pocket, gone live, recorded stuff, sent it to Google's servers, realized it wasn't a valid query, and shut off without alerting me. I've certainly seen the Assistant dialog randomly open when looking at my phone plenty of times, which is usually a good indicator that such a thing has happened. If it silently fails in such a way that the UI doesn't respawn, then I would have no idea at all.

The net effect is that Google gets a random sample from billions of random conversations from millions of people every time this thing unintentionally goes off. They have a clear explanation as to why they got it and why ads are being served in response afterward. They can even make the case that the system is functioning as intended - after all, it'd be unreasonable to expect no false positives, or program bugs, or whatever, right? They can even say it's the user's fault and that they need to tune the voice model better.

Regardless, none of this changes the net result, which is they get a random sample of your conversation from time to time and are allowed to do whatever with it that they would have done if you sent it on purpose.

I don't know - where is the proof it's not? It's not like I can look at the source to the ad SDKs and figure out what they're doing.

It's much better and safer to assume they are than they're not, especially because I've seen many many results which indicate they are.