Message handover for networked beacons

A data transmission system comprises a first (12) and two or more second (13, 14, 15) beacon devices interconnected (11) as a cluster capable of wireless message transmission, and at least one mobile device (10) capable of receiving such message transmissions. The first beacon (12) is arranged to broadcast a series of inquiry messages (INQ) according to a first communications protocol, such as Bluetooth. The mobile device (10) detects such inquiry messages and replies with an identifier for itself. The link (A) from the first beacon device is then re-established between a selected one (14) of the second beacon devices. When a handover trigger event occurs, paging and page response messages are used to select a further second beacon device (13) and transfer the communications link (C) thereto.