Nearly....it's worse than that, though.
The key point to take here is that my smartphone's acting as an
independant input device, with a seperate (apparently-irrepressable) software instance of Google Assistant on a device which is being thought of as being just an administration/control tool rather than a voice conduit.
Let me put this another, simpler, way.
All hardware smart-speakers appear to be fitted with a physical microphone mute switch. Conversely,
no smartphones are similarly-equipped. So you're looking at your smart-speaker, thinking you've 'turned its ears off'....which you have, but entirely irrelevantly-so. Because there's a completely-seperate audio path via another independant Google Assistant instance, in your pocket.
This is NOT nearly as straightforward as it sounds (if it were, this thread wouldn't have been opened). The settings options vary between apparently-identical models smartphones with what would be expected to be the same software.
I suspect (no, hope, in my case) that what may be happening for users of some smartphones is that the exact combination of application software as installed is causing unwanted permissive effects. For example, my Samsung phone already had an application on it from new called "S Voice", and I am not sure I can safely remove that unused app....but it may be relevantly interfering with this effect.
Also (something anyone with a smartphone will relate to) there are
numerous graphically-represented faders & level controls designed into the GUI for eg audio settings.
These attempt to make life simple for users of mobile devices, but in practise they all tend to blur the boundaries between what can be: 'Media Volume'/'Ringtone Volume'/'Source Volume'/'Audio Level'. I bet
everyone here with a smartphone of any flavour has had occasional challenges in getting (and keeping) these controls set.
Another Achilles heel on smartphones is (I strongly suspect) the soft button that's intended to mute/unmute the smartphone's microphone *during phonecalls*. I am convinced that either clumsy coding (or application compatibility/conflict) means that sometimes the action of toggling the phone's mute-button to 'unmute' can reenable the local ambient audio pickup within a speech-to-text Google Assistant type of search app.
(I also do wonder whether the universal utility within smartphones to be able to 'cast' media content to localised smart-speakers via either Bluetooth or Wifi local loop is another unwitting conduit via which ambient live speech is being either occasionally routed, or, accidently enabled.
Similarly, if you ever use your smartphone to make voicecalls via eg Facebook Messenger, or other toll-free "wifi call apps" such as Zoiper, since this enables two-way audio path operation outwith the context of conventional mobile phonecalls, the action of so doing may collaterally-reactivate previously-disabled audio settings).
@Mythopoeika /
@Analogue Boy - please re-read my rambling-but-consistent tale above.
I am trying to emphasise that the conduit for this unconsented accidental broadcast of intimate personal trivia (or corporate intel) is NOT necessarily one of these overt Google Assistant/Alexa smart-speaker 'upholstered rocks' that you've (perhaps justifiably) decided to exclude from your home.
I'm saying that the tenant in your household which may now be impassively-transducting your harmless daily prose could well just be your phone, your laptop, desktop or tablet computers.
Unless you've just got a silver Nokia brick from circa 2004, and still a WindowsXP door-stopper, there is a tangible technical
potential for the contemporary replacements for these classic originals to be reporting your every creak and croak.
I'm not proposing paranoia. Or the Luddite flushing of phones and speakers down the toilet. Because the technology is omnipresent and useful. But we do need to be given proper handles for this, by technologists....that work.