Article Written for:  Forbes.com

If you have an Amazon Echo, try this: Say, "Alexa, tell me a joke," but do it very quickly so that you finish the request before Alexa "wakes up" (indicated on the Echo by the blue light). Did you notice that Alexa dutifully complied, seemingly catching the request before she (it?) was awake? There is a simple explanation for this: Alexa (like other artificially intelligent digital assistants) is always listening. Indeed, Alexa starts recording "a fraction of a second” before the wake word. Google Home listens to snippets of conversations to detect the "hotword."