Amazon updated their Alexa sample code on GitHub with a new wake word engine. This means that if you'd like to make your own Amazon Alexa with a Raspberry Pi, you can do so without the previously required press of a button.
The previous version of this project required that you press a button or an on-screen prompt before you could ask Alexa a question. Now, you can do so with a wake word, like "Alexa," just like you can in the commercial version of the Alexa. This makes the prospect of building your own Alexa a heck of a lot more useful. As before, you'll need a Raspberry Pi (model 2 or 3 are recommended, though we've seen the previous version running on both a C.H.I.P. and a Zero), USB microphone, and a speaker. You'll find everything you need to know over on Amazon's GitHub page.
Alexa AVS Sample App [GitHub]