I saw a video circulating on the internet about Samsung phones (i.e. any Galaxy) having a layer of plastic that includes a circuit board inside wrapped around the device battery. The plastic layer is found just underneath the label of the battery (where you see the Samsung logo). Unwrap this and then un-stick the plastic layer with the circuit board.
People have said that this plastic serves for nothing (the phone works perfectly without it) and that it is used to eavesdrop people.
I am not sure who to believe but better be safe than sorry.