I'm pretty sure that's not what's happening with the devices.
The phone or device listens for wake words. "alexa" "ok google" "Hey siri". It doesnt send anything to the servers until it hears those words. Sometimes it may *think* its wake word was triggered by a similar sound and you'd get some additional recordings.
But that's hardly "tech employees can listen in at any time"
I was exaggerating and probably shouldn't have said "literally," but there's very little distance between pulling up your past audio clips and listening in whenever they want.
I know that sounds a little tinfoil-hat-esque, but if the news broke tomorrow that Facebook was using these devices to record huge chunks of what happens in someone's home, whether they're "activated" or not, or even watching/listening in people's homes in real time, would anyone be surprised? Of course not. These companies have given no indication they have the ability to restrain themselves.