XDA Senior Recognized Developer ” has released a new Android app called Pry-Fi, that allow a user to disable Wi-Fi completely, including the background network scanning. The app will prevent your device from announcing all the networks it knows to the outside world, but it will still allow background scanning and automatically connecting to networks. Even when your phone is turned off, your phone may be broadcasting information to whomever is in range which can be used both to track repeated visits to as well as your exact movements in an area under surveillance.
Source: https://thehackernews.com/2014/02/chainfire-released-pry-fi-android-app.html