The Selective Calling (SELCAL) System monitors all of the communications radios. When the system receives a properly encoded call from a ground station, the crew is alerted through the illumination of the corresponding light on the pilots call panel.
As installed - Communication Crew Alerting System
The flight crew is also alerted to an incoming call by an aural chime and the •SELCAL communication message on EICAS. The flight crew should respond by pushing the corresponding switch on the pilot's call panel or by transmitting on the corresponding radio.