An optical hookswitch assembly useable on a telephone set as an optical communications port is disclosed. The hookswitch assembly is comprised of light emitting and detecting diodes so disposed in the telephone so as to detect the presence of a handset. A processor connectable to the telephone circuitry...http://www.google.com.hk/patents/US4847900?utm_source=gb-gplus-share專利 US4847900 - Infrared hookswitch for a telephone
