This part of IEC 60839 specifies the requirements for standard interfaces using a two-wire connection employing ISO/IEC 8482 signalling for use between the control and indicating equipment (CIE) of an alarm system and one or more alarm system transceivers connected to alarm transmission systems. This standard provides a flexible interface allowing the connection of a single master CIE to a number of devices in accordance with ISO/IEC 8482 which may be alarm system transceivers or slave CIE. This is required in order to ensure compatibility of equipment from different suppliers. The standard applies equally to the transmission of alarms and other messages to/from intrusion, fire and social alarm systems, and to the transmission of information to/from other similar systems.