A dual-mode controller may include a communication interface between a handheld electronic device and subsystems on a computing bus or network. The dual-mode controller may operate in a “master mode” when a user directly manipulates the dual-mode controller to communicate with any subsystem(s). In this mode, the dual-mode controller may serve as a master controller and accesses and controls various subsystems on the bus or network (such as audio/visual subsystems, temperature control subsystems, alarm subsystems, sensors and transducers) as a master controller. In a slave mode, the interface may act as an adapter or interface between the handheld device and the subsystems.