A wearable device worn on the head of a user determines the head orientation of the user. A tracking application executing on the wearable device determines the orientation of the wearable device relative to a frame of reference. A mobile application executing on a mobile device likewise determines the orientation of the mobile device relative to the frame of reference. The frame of reference may be magnetic north or an inertial reference frame shared between the wearable device and the mobile device. The tracking application estimates the head orientation of the user, relative to the mobile device, based on the relative orientations of the wearable device and the mobile device.