A communications system comprises at least one beacon device (12, 14) capable of wireless message transmission and at least one portable device (10) capable of receiving such a message transmission. The beacon (12) is arranged to broadcast a series of inquiry messages (60) each in the form of a plurality...http://www.google.de/patents/US20020016165?utm_source=gb-gplus-sharePatent US20020016165 - Localised audio data delivery
