WatchConnectivity
Now you can take advantage of robust device-to-device communication between the WatchKit extension on Apple Watch and the containing app on iPhone. WatchConnectivity enablesApple Watch to communicate directly with known wifi hotspots using the new Tetherless Wi-Fi feature in watchOS 2. This keeps your Apple Watch app up-to-date, even out of range of the iPhone. WatchConnectivity also saves battery life by allowing the WatchKit extension to transfer new information for the iPhone app to use when it’s next launched, allowing for seamless file transfers between the Apple Watch app and iPhone app.