When developers need to communicate directly with users, push notifications provide the solution. They deliver messages directly to the iPhone screen via a special Apple service. Push notifications let the iPhone display an alert, play a custom sound, or update an application badge. In this way, off-phone services connect with an iPhone-based client, letting them know about new data or updates. Unlike most other iPhone development arenas, nearly all the push story takes place off the phone. Developers must create Web-based services to manage and deploy these updates. In this chapter, you learn how push notifications work and dive into the details needed to create your own push-based system.