A communication protocol for use between serially chained portable pendant peripherals and a portable host device. The bus communications system protocol enables multiple low power input/output peripherals to communicate over a bi-directional data line with a portable host device such as a PDA or cellular phone. A message packet data structure for use in the bus communications system includes a device identifier, a packet type identifier, and message data bits. The packet type identifier describes the actions associated with the packet. A method determines whether the message packet received by a device is intended for the device by evaluating if the device identifier is zero. If the device identifier is other than zero, the method modifies the device identifier and communicates the message packet to another device in the bus communications system.