I don't think Alexa nor the Google homes listen and send data to the respective "motherships" at all times.

Both do local processing for the keywords until it hears one then sends the following data (and I believe a few seconds prior) to the servers for processing.

My phone works the exact same way with the Google assistant. I don't know if other "assistants" (like Bixby) work the same way.

The smartphone is their; I mean, your GPS tracker for machine learning movement behavior. Voice (various project names), Text (SMS gateways) and Data (CarrierIQ) are just a value added bonus.

I enjoyed the conversation with Alex Stamos (former CSO at Yahoo/FB), where pointed out that had George Orwell been told that people would willingly pay for a tracking device and keep it on them at all times and powered on at all times, he would not have believed it.

I should add, any time I say anything even remotely negative about cell phones, I get beat up here at HN pretty good. This is a very good psychological indication that people have cognitive dissonance and denial around this topic.