GCM Client App on Android - https://developers.google.com/cloud-messaging/android/client
android sample - https://github.com/googlesamples/google-services/tree/master/android/gcm/app/src/main/java/gcm/play/android/samples/com/gcmquickstart
other devices
Set up a Client App on iOS
https://developers.google.com/cloud-messaging/ios/client
Implement a Client App on Chrome
https://developers.google.com/cloud-messaging/chrome/client
origin - http://www.pipiscrew.com/?p=4340 gcm-registering-client-apps-push-notification