Orientation determination for a mobile device

A system for determining an orientation of the head of a user of a mobile device comprises a head-mounted accessory device including a first digital compass for providing a first orientation signal and a short-range wireless transmitter for transmitting the first orientation signal to the mobile device. The mobile device includes a receiver for receiving the first orientation signal. A processor in the mobile device determines the orientation of the user's head based on the first orientation signal. The mobile device may include a second digital compass, thereby providing greater accuracy. By comparing the two orientation signals, the device can infer whether the user is viewing the mobile device. Tilt sensors in the accessory device and mobile device can also be used with the orientation signals to infer whether the user is viewing the mobile device and thus to control content delivered by the mobile device.