Introducing Push Notifications

Push notifications, also called remote notifications, refer to a kind of message sent to iOS devices by an outside service. These push-based services work with any kind of application that normally checks for information updates. For example, a service might poll for new updates on Facebook, Twitter, or Google Plus, scan for nearby dangerous weather systems, respond to sensors for in-home security systems, or invite you to a game match. When new information becomes available for a client, the service pushes that update through Apple’s remote notification system. The notification transmits directly to the device, which has registered to receive those updates.

The key to push is that these messages originate from outside the device itself. They are part of a client-server paradigm that lets Web-based server components communicate with iOS clients through an Apple-supplied service. With push, developers can send nearly instant updates to iOS devices that don’t rely on users launching a particular application. Instead, processing occurs on the server side of things. When push messages arrive, the iOS client can respond by displaying a badge, playing a sound, and/or showing an alert box.