A wireless short range radio-frequency master device adapted to create and maintain a portable private network of wireless short range radio-frequency slave devices wherein the master device is configured to detect and register suitable slave devices for a network, and is capable of determining the proximity of any registered slave device with respect to the master device in use, the master device further being adapted to enable a user to define two or more groups of registered slave devices selected from the total number of registered slave devices and to enable a user to select a defined group of such registered slave devices as an active group, thereby forming an active portable private network of wireless short range radio frequency devices comprising the master device and selected registered slave devices within the selected group.