Amazon Echo Privacy: Is Alexa listening to everything you say?

When Amazon released its voice-controlled personal assistant in November 2014, an important question was raised about the hands-free speaker: if the Amazon Echo is voice-controlled, then is it always listening? Essentially, all voice-controlled assistants — Apple's Siri, Microsoft's Cortana, Google's AI assistant, etc. — work the same way: The device activates once it detects the "wake word." For the Amazon Echo, the wake word is the assistant's name, Alexa. But in order to detect its name, the Echo has to be listening in at all times on some level.