This European Standard specifies requirements, test methods and performance criteria for input/output devices connected to a transmission path of a fire detection and fire alarm system, used to receive and/or transmit electrical signals to or from the transmission path, necessary for the operation of the fire detection and fire alarm system and/or fire protection system. An input/output device may be a physically separate device or its function may be integrated into another device in which case this European Standard may be used to assess this function. Control and indicating equipment, and ancillary control and indicating equipment (e.g. repeater panels and fire brigade panels) are not covered by this European Standard.