Ambient mode uses the microphones in your headset to enhance your surroundings. You can use this feature when you want to hear more of your surroundings or have a conversation with your headset on.
1

Slide the Noise Cancellation switch on the right ear cup up to AMB to turn on ambient mode.

Cisco Headset 730 noise cancellation switch
2

Slide the Noise Cancellation switch to OFF to turn ambient mode off.