Update:

• The Camera Circle feature is now available for everybody. (Previously, it was in beta.)
• Use it for quick looks outside the headset or for picking up the controllers after putting on the headset.
• Cam Circle can auto-start when it detects you're wearing the headset.
• On a Vive Pro and Index the pass-through video can be in 3D. On a Vive it's monoscopic (2D).
• All Cam Circle options can be set by a few checkboxes on the SteamVR dashboard page.
• Start Cam Circle manually either by double tapping the headset or by pressing both grip buttons simultaneously.