Notifications iniOS provide a way to notify the user when a particular application-specific event is happening when the application is not in the foreground. For example, if you're building an instant messaging application, you might want to let your users know that they've received a message, even though they might have another application open, or even have the phone in standby mode. If your application is in the background or not running at all, the user can be presented with an alert message, or you can badge the application icon. You can even play a sound in addition to the alert message. For example, when you get a new mail message, the Mail Application's icon badge number increases by 1 and a sound is played.