A method and system are provided for controlling which communication interface is used for communication between devices that are configurable to be part of a wireless body area network (BAN) for a medical device system depending on their respective locations with respect to a first device. Based on a security secret shared between the first device and a second device, a secure communication channel can be established between the first device and the second device when the second device is located in a coverage region of the wireless body area network. A controller can determine, whether a quality of service (QoS) over the secure communication channel is greater than or equal to a first threshold. In response to the controller determining that the QoS is greater than or equal to the first threshold, data can be communicated from the first device via magnetic signals using a first BAN communication interface.