THE AMAZON ECHO can seem like your best friend---until it betrays you. That's because this device is different from anything else in your house. Alexa, the voice assistant that powers Echo and more, is always listening, sending what you say after using a "wake" word to Amazon's servers. Of course, Echo isn't the only voice-assistant speaker on the market, but it sits in millions of homes, and Alexa is headed to devices from companies like Ford, Dish, Samsung, and Whirlpool.
