Recently FUD stories like this have spread as a result of incomprehensible terms of service wrapped in so much legalese that no one knows what they're really agreeing to. This time however, the fuel appears to be app permissions on Android and iOS. While Facebook does list a permission to use the microphone on iOS and Android, it's only activated when a user tries to identify something like music or a TV show.

Unfortunately, most people aren't sure what the permissions mean -- even an app like Skype with an obvious need for access has to explain it -- and assume anything listed might be in use at any particular time, no matter how unlikely that is. That said, if you do want to make sure Facebook does not have access to your microphone, you can disable it on either mobile platform. On iOS, just go to settings, select Facebook, and move the slider for microphone to off, or on Android, if you look under Apps in the settings menu, find Facebook and select permissions, you should see a similar slider for the microphone.