Appliance Science: How Alexa learns about you

In my last column, I looked at how Amazon's Echo device and the Alexa voice service allows you to control things with your voice. You speak, it understands and obeys. Alexa is just part of a new wave of services that allow you to control things with your voice, from cell phones to intercoms and thermostats. You can even do things now like ask her to start your car. So, how do these listening devices transform your mellifluous voice into computer commands?