Apple released new Smart watch recently so iOS App developers gets ready to develop innovative apps for apple watch. Learn how you can bring your existing app notifications easily on Apple Watch. And by leveraging WatchKit, you can take your apps even further by extending and enhancing their functionality on Apple Watch.
Recently Apple release Xcode 6.2, including iOS 8.2 SDK with WatchKit developers can download from below link its totally free
A WatchKit extension that runs on iPhone and a set of user interface resources that are installed on Apple Watch. When your app is launched on Apple Watch, the WatchKit extension on iPhone runs in the background to update the user interface and respond to user interactions. WatchKit provides three opportunities to extend your iPhone app to Apple Watch: WatchKit apps, Glances, and actionable notifications.
for more info visit Apple watch site click here