title: Android: Receive Push Notification when the App isn't running
body: <p>I am looking to implement push notifications in my app.  I have already sent notifications from inside the application's context, but I want the user to receive notifications when the app isn't running.  For example, you receive a Twitter or Facebook notification when you have a new message, but the Facebook app isn't open or running.  I will be reading data from a server.  When the server sends out a message, I want the user to get the notification, whether the app is open or not.  I have looked at <code>Service</code> but couldn't find anything promising.  Any ideas?</p>