If you do not have a server, I think what you are looking for is to implement an Android Sync Adapter. You can learn more about the SyncAdapter class from this link: http://blog.udinic.com/2013/07/24/write-your-own-android-sync-adapter/ .
If you have a server handling the communication, you may want to use Google Cloud Messaging, and use Push to push unsynchronized data. You can check examples at https://developers.google.com/cloud-messaging/ .