You may have ignored this in the past but some apps in your phone usually have ridiculously long permissions on some of your phone resources like the camera, location, text messages and microphone. Facebook is one of those apps and due to the fact you may have inadvertently granted it permission to access you microphone, it can actually do a Shazam function with that.
On Facebook Help center for the Android App, someone posted:
“Does Facebook record conversations when it identifies the things i’m listening to or watching?”
In a world where privacy online is valued, this would be a normal question to ask since the Facebook app has access to your microphone. Facebook responded by clearly stating the app does not record your conversations and it will only be active when you are writing a status update.
So why does Facebook need the microphone access? Apparently it was revealed that when you turn on the feature, it will be able to identify what you are listening to, whether it is music or a TV show. The feature can be activated in the process of writing a post where you tap the 
button and later on the 
button to toggle it on. As it identifies what you are listening to, the 
icon will animate and once there is a match, it will display this notification 
. If you are unable to get a match, you can just refresh using the drag to release gesture.
Now for the sad news. This feature is only available in the US which is a bummer albeit not surprising since we have seen other tests being made like the Local Markets one. It would be cool if this was rolled out to everyone.
