Due to the nature of mobile devices, they are often used in situations where visual feedback is not enough to get the user's attention. Unlike desktop computers, mobile devices are usually powered on all the time, but not in active use. Therefore, incoming calls, chat sessions and other events may benefit from using non-visual feedback, such as vibration or sounds. The type of feedback can be adapted to device or application state. For example, when the screen is inactive, the device can be assumed to be away from the user, such as in their pocket or bag.
For more information on non-visual feedback and how to use it, see Non-visual feedback in MeeGo 1.2 Harmattan developer Library.