Sub Handset - Sub handset to communication with maximum two IE series door station. Door call-in is announce with either a two or four stroke chime. The IE-8HD features a handset for private communication, selective door release control, chime volume control and selective calling to sub handsets (IE-8HD). Maximum five IE-8HD can be connected in a system an IE-8MD must be included as a master handset when using the IE-8HD.