How would you activate certain voice commands if it wasn't listening to all?
If the microphone was off than it has no way of hearing and activating the commands. So by design it's microphone needs to be on 24/7.
You could have a push-to-talk button on a remote control to enable the mic but than you just might as well use the remote control.
All these talk to activate features are designed only for the sake of being gimmicky and unethical surveillance.
Smart TVs might work similar, but I surely won't have anything like it in my home anyway.
But like I said, I don't want to have those devices either and my smartphone has a removable battery ..
One common implementation is to use a locally detected wake word (described in another post), but I've also seen many which require you to hold down a button to speak voice commands. Both solutions answer your technical question satisfactorily.
However, this is how I (and most people) expect voice commands will work based on plain reading of the fine print: the voice commands will be transmitted, but it won't establish 24/7 audio surveillance of your house.
The fine print (and therefore the "explicit" "consent" so obtained) is deceptive and fraudulent.
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However your real concern is apparently a trust question, not a technical question. That technical question was apparently just a distraction.
Obviously if you don't trust the implementer not to lie about their implementation (ie you assume fraud at the outset), then any microphone (or speaker for that matter!) could be a 24/7 listening bug regardless of trigger implementation or EULA fine print. I see that in another reply you already moved the goalposts thusly.[1] :P
Sure there is. I would expect a feature called "Voice Recognition" would only be active when I was using voice commands (and perhaps the occasional accidental activation), but not at other times.