Head-mountable apparatus and systems

摘要

A head mountable device 20 comprises an orientation detector (730, figure 17) operable to detect whether the orientation of the head mountable device is in a predetermined range of orientations; and a signal emitter (810, figure 19) operable to emit a signal, for detection by a base device (820, figure 19) separate from the head mountable device, in response to a detection that the orientation of the head mountable device is in the predetermined range of orientations. Alternatively, signal detection is carried out in response to a preselected orientation of the head mountable device. The signal emitter comprises one or more sound sources, or one or more radio sources. The range of orientations is around a vertical orientation and / or around an orientation directed towards the base device or another point. The base device may comprise an array of two or more detectors (650, figure 14) or a phased detector array.