I looked into Alexa's inner workings after some of the posters above questioned the privacy aspect and am reasonably satisfied. Their admittedly self-interest documentation says that Alexa only listens for one word, Alexa, and then wakes up.

I will say this is the most enjoyable thing I have bought in a long time. I am now experimenting with "Alexa, play the top 100 songs from 19xx" starting from my birth year to present in ten year increments. It is interesting how the music has noticeably changed and the memories it brings back.