A method for concerted synchronisation of data across a wireless mesh network arrangement; the wireless mesh network arrangement comprising a control panel, a receiver and a plurality of network devices (11, 12, 13); wherein: the control panel transmits a message to the receiver, said message comprising a list of network devices (11, 12, 13) that the control panel needs to synchronise with; the receiver identifies a suitable target device from the list of network devices sent by the control panel, to which to direct an outgoing broadcast message and then wirelessly sends the outgoing broadcast message to the target device, via devices that are on a predicted route of communication between the target device and the receiver; wherein the outgoing broadcast message comprises the list of devices that are to be synchronised with the receiver and control panel; wherein each device, on the predicted route to the target device, that forwards the outgoing broadcast message switches to a receive mode after forwarding the message; wherein adjacent devices that are not on the predicted route but that are identified in the list of devices that require synchronisation, as specified by the control panel detect the message and respond to it with a short broadcast acknowledgement message that comprises their current status information; wherein said devices on the predicted route then receive and collate the short broadcast acknowledgement messages received from the adjacent devices to produce an array of device data for all adjacent devices from which they have received a response; and once the last device on the predicted route has forwarded the outgoing broadcast message to the target device, and finished its receive mode window, the last device produces a broadcast acknowledgement comprising all of the collated short broadcast acknowledgements received from adjacent devices, as well as its own data; wherein this broadcast acknowledgement is then sent back as an incoming message to the receiver via the same route as taken by the outgoing broadcast message; and wherein devices that forward this incoming broadcast acknowledgement to the receiver also add data from the acknowledgement messages that they have received from adjacent devices, as well as their own data. the control panel transmits a message to the receiver, said message comprising a list of network devices (11, 12, 13) that the control panel needs to synchronise with; the receiver identifies a suitable target device from the list of network devices sent by the control panel, to which to direct an outgoing broadcast message and then wirelessly sends the outgoing broadcast message to the target device, via devices that are on a predicted route of communication between the target device and the receiver; wherein the outgoing broadcast message comprises the list of devices that are to be synchronised with the receiver and control panel; wherein each device, on the predicted route to the target device, that forwards the outgoing broadcast message switches to a receive mode after forwarding the message; wherein adjacent devices that are not on the predicted route but that are identified in the list of devices that require synchronisation, as specified by the control panel detect the message and respond to it with a short broadcast acknowledgement message that comprises their current status information; wherein said devices on the predicted route then receive and collate the short broadcast acknowledgement messages received from the adjacent devices to produce an array of device data for all adjacent devices from which they have received a response; and once the last device on the predicted route has forwarded the outgoing broadcast message to the target device, and finished its receive mode window, the last device produces a broadcast acknowledgement comprising all of the collated short broadcast acknowledgements received from adjacent devices, as well as its own data; wherein this broadcast acknowledgement is then sent back as an incoming message to the receiver via the same route as taken by the outgoing broadcast message; and wherein devices that forward this incoming broadcast acknowledgement to the receiver also add data from the acknowledgement messages that they have received from adjacent devices, as well as their own data.