An inbound call centre.

To provide a visual indication of incoming call density, four Universal Alarms were used with the exchange line inputs wired across the second-last, fourth-last, sixth-last and eighth-last incoming exchange lines. The outputs were connected to green, yellow, blue and red strobes mounted together on a panel. As the waiting call queue became longer, the strobes would flash giving supervisors and workers a visual warning of a peak in the incoming call rate.