A free app for Android, by MSAPPZ.

Internet(Data/Wifi) Lock Lite is the best tool for the purpose. The application is capable of locking Wifi and Data connections. This app provides a way to protect your network from unauthorized access. The tool will enable you to set a password that will enable you to access the network only if you enter the correct password.

The app can be used with your Android device and has the ability to protect both Wifi and Data connections. With this tool, you can protect your network from unauthorized access. 

This application can be used in situations where you have an unlimited plan at your home or office. The tool can be used with both Wifi and Data connections. The user has the option to protect Wifi only, Data only, or both.