For persons who are deaf or have a severe hearing impairment it is essential that they can see some form of visual signal for incoming calls. Visual signals incorporated in the terminal are not easily seen and are mainly of use as a reminder of line status. Socket connections should be provided so that external indicator lights can be powered from the terminal, either directly or from the mains supply through a relay. Alternatively, systems which cause the domestic lights to flash can be used. Vibrating pagers are an alternative to flashing lights.
Telephone features that make a difference .