Group car station is for security room or for building management room which is central for large complex security management. These devices can be connected to multiple car at one place to communicate from single station.

Car station also called as slave station is used for push to talk from inside car. Person trapped inside need to push alarm / intercom button to get attention for people in lobby once they pick up the received call get established and passenger can remove the finger from button and talk has 3 models

Lobby station also called as master is used for receiving call from slave or car station intercom. In 3 way connection one of this is kept in lobby and one in machine room while slave will be inside elevator car This can function in pair of master slave, two master can not communicate together