Well they don't have big hard drives, so you can be confident they're not recording everything to disk that then could be unintentionally accessed or sent out l

Well they don't have big hard drives, so you can be confident they're not recording everything to disk that then could be unintentionally accessed or sent out later. And you can look at network traffic (e.g. from wifi router stats) to be pretty confident they're not constantly live-streaming audio up to the cloud. Of course most people will not actually do this monitoring themselves, but there are enough of these devices out there that if a significant number started recording constantly somebody would notice pretty quickly. And that would be terrible PR for the company involved, so I think google and amazon and apple have a pretty strong incentive not to do this.