Article: However, if you are not currently using the internet but your device is on, its best to turn off your Wi-Fi adapter.  If your device has an internal Wi-Fi adapter, you can access Network Connections on Windows by clicking Start, typing “ncpa.cpl” and pressing Enter on your keyboard. Note: The process of disabling your Wi-Fi card will vary from device to device. Consult your manufacturer documentation to learn more. On Mac OS X, click the Apple menu in the upper left corner followed by “System Preferences”> “Network”>”Turn Airport Off”. If you have an external Wi-Fi card you can simply remove it from your device.

What is a summary?
Most modern PCs and mobile devices will automatically connect to a wireless network when it’s in range.