Google terms of service (and I assume also Apple and Amazon) are clear. If they go against that, they would be opening themselves to a HUMUNGOUS lawsuit. Basically, the devices (I have Google Home) listen but do not record. When they hear the activation phrase, they monitor what comes next to parse out (and comply with) the request/instruction/query. That then appears as an event in your Google Home history (which you can delete, if you want).
In principle, yes…they could eavesdrop on everything you say. In practice? Why would they? It would require HUGE amounts of processing power to get anything from it, it would open themselves to a lawsuit, and the pay-back would probably be non-existent.
We have a Google Home device, another “speaker”, plus a Google Mesh router with 2 repeater points. Those two points also respond to commands just as the Google home devices do. So we have four active speakers in the house. We have several lights, the robot vacuum, and the Chromecast connected to it. Very convenient. When I say “goodnight”, it makes sure everything is off (that is connected to it).
I do agree that I’m not particularly interested having the fridge or other appliance connected to WiFi. We have one thermostat that is, but it’s not in Google Home. Trane has a separate app. Though I usually just walk up to the panel if I want to look or change something. I also don’t want door locks on the WiFi (which seems to be a “thing” recently). A key is just fine with me, and probably more secure. If I had to replace my irrigation timer, I might go for one with WiFi. Maybe.
1poorguy