This Line of Door Speakers Have a Voice Communications Interface that Mounts Adjacent to an Entry Door. Two-way Voice Communication with the Resident Occurs Through the Unit"s Built-in Speaker. The Door Station Mounts Recessed in the Wall Using an NRKR300D Door Speaker Rough-in. This Series of Door Speakers are for Use with the NM100 and NM200 "Master" Stations Only. NuTone NDB300 NM Series Intercom Door Speaker Features a Lighted Chime Pushbutton 4-3/16" W X 6-5/6" H X 1-3/8" D