A security system comprising a plurality of security subsystems each of the security subsystems being discretely located, typically in separate buildings. The security subsystems are interconnected by a system communications bus to enable bi-directional communication between the security subsystems. Each of the security subsystems comprises a user interface, a control panel, a plurality of security devices, a local communications bus, and a panel linking gateway. The panel linking gateway allows data on the local communications bus of each security subsystem to be transmitted to and received from the system communications bus. The security system allows a keypad or other user interface from one security subsystem to access and control a second remote security subsystem.