I am looking to write an app that receives pushed alerts from a server. I found a couple of methods to do this.
You can use Pusher
It's a hosted service that makes it super-easy to add real-time data and functionality to web and mobile applications.
Pusher offers libraries to integrate into all the main runtimes and frameworks.
PHP, Ruby, Python, Java, .NET, Go and Node
on the server
JavaScript, Objective-C (iOS) and Java (Android)
on the client.