Abstract: A system comprises a computer device, such as a host apparatus, a second device, such as a digital signage player, which is connectable to the computer device, and an external device connectable to the second device. The computer device sends a command to the second device. The command causes the second device to send a message to the external device. The command includes destination information for the external device and a command payload, whereby the second device can be controlled to send a message to the external device corresponding to the destination information with a message payload corresponding to the command payload and compatible with the external device.