You can do multiple runs of feeding pre-recorded messages into say multiple speakers and do the trial over many days. Then on a series of other speakers you can do a robust sequence of pre-recorded conversations followed by the same pre-recorded messages at the same time and then do statistical analysis on traffic volume.
I just presume these things are listening to everything and recording everything. I think that should be the general assumption if you bring essentially an "internet microphone machine" into your home.
If not by the company who sold it to you then by 3rd party hackers, clever app developers, or some other group. Every marketer wants to know what their customers are saying in the privacy of their own home.
As a tangent I've long wanted to have fun with this ... start a campaign to start collectively talking about a ridiculous product (say a vacuum cleaner with elephant ears that flap in proportion to the amount of dirt it picks up) in private conversations and see if a company releases it by listening in. "There's significant consumer demand for the dumbo-vac!"