You can trust them as much as the manufacturer of your phone. No difference there, phones could also always listen.

I'm starting to get tired of this. I really don't understand this sentiment on a forum called "hacker news" of all places. You don't have to trust anyones word about it not listening 24/7. It is t r i v i a l to look at the data from the echo transiting across the network. You can see that the traffic spikes after you say alexia as it sends the audio data out.

If they lie about this in general(and enable blanket surveillance), it would be relatively easy to detect , and hurt Amazon's brand.

How? If you say "by analysing the amount of data it transmits when not in use", then not really - they could record it locally and then sneak it alongside a normal request.

I don't know how Echo's update, but they potentially could also sneak in an update that does listen 24/7, then a couple days later push an update that turns that off.