Often you want to use the Cortex Alarms but mute the VHF radio so that only an alarm will sound but you will not be awakened to VHF chatter. You can do this from the VHF view. Tap the speaker icon. When the speaker is displayed red with a strike through, the VHF is muted, but all Cortex alarms will still sound.
The mute control can also be accessed from any other screen by pressing the volume key on the right side of the handset, and applies to both the Hub's external speaker and all connected Handsets.