• Each DX121 Base Station supports one beltpac/communicator in full duplex, hands-free operation and supports up to four registered beltpac/communicators. (but only one beltpac/communicator  may talk at any time)
Additional Info:
The DX121 2.4 GHz Wireless Intercom System 
The Base Station will connect to a dynamic microphone headset jack or a 4-Wire connector of a hardwired intercom station, and also provides battery-charging capability for one battery. The system typically uses BP200 Beltpacs, but can also be used with the WH200 All-in-One Headset communicator and/or WS200 Wireless Speaker Station. Once connected to your system, you can leave your console or intercom station while using a beltpac/Communicator and or Wireless Speaker Station .
• Compatible with RTS and ClearCom/Production Intercom wired intercom headset or 4-Wire capable equipment.
NOTE: Use only with headset connectors capable of supporting dynamic microphone headsets.
• In the default mode, the ISO button activates relay-controlled contacts.
• The IC button activates audio to the 4-Wire and headset Input/Output connector(s).
• The ISO and IC buttons activate audio to other registered Communicators.
• The Base Station can charge a BAT41 battery in less than 3 hours.
• In case of power outage, the Base Station will operate temporarily from a battery in the charging port, for approximately 30 minutes.
The quick start guide for the DX-121 system is attached below.