The NA3003C 3-Note Chime Module Can Be Installed in Either NM100 or NM200 "Master" Stations. To Announce a Visitor, the Intercom System"s Door Chime Sounds When the Chime Button is Pressed On a Door Speaker Connected to the Intercom. The Module Can Be Set to Play One, Two, or Three Notes with a Different Chime for Each Door. NuTone NA3003C Intercoms 3-Note Chime Module Chime Module Mounts Inside "Master" Station 3-1/4" W x 3-1/4" H