https://www.theverge.com/2018/5/24/17391898/amazon-alexa-private-conversation-recording-explanation

Amazon has been forced to explain how Alexa recorded a private conversation and sent it to an Echo user’s colleague without their knowledge. A Portland woman identified only as Danielle revealed the odd series of events in an interview with local TV station Kiro 7, claiming that an Amazon Echo device recorded a private conversation between her and her husband and sent the recording to an employee of the husband. In a statement to The Verge, an Amazon spokesperson confirmed this incident took place, but it appears it was an unusual series of Alexa mistaking conversation as commands rather than Alexa spying on users.

“Echo woke up due to a word in background conversation sounding like “Alexa.” Then, the subsequent conversation was heard as a “send message” request. At which point, Alexa said out loud “To whom?” At which point, the background conversation was interpreted as a name in the customers contact list. Alexa then asked out loud, “[contact name], right?” Alexa then interpreted background conversation as “right”. As unlikely as this string of events is, we are evaluating options to make this case even less likely.”