When sound detection is on the camera will listen for loud disruptive sounds that may be in or outside of the cameras view.
To turn on and off, open camera settings by tapping the name of the camera on your home screen, or by tapping the gear icon on the top right of the livestream screen. Scroll down to "Notifications" and tap to view the notification options. Toggle Sound Notifications on or off. Go back to Camera Settings and tap "Event recording" to view the recording options and toggle sound on or off.