See-through mode is designed to be triggered in any of these ways:
- Safety visuals. When a user approaches a virtual boundary of relative to the center of the established virtual space, the standard gray “safety fog” will start showing an image from the camera to increase awareness of surroundings. 
- Controller connection and recovery. If controllers are disconnected, see-through mode will be automatically enabled to make it easy for the user to reach for and turn on controllers without removing the headset. 
- Experimental see-through mode apps. Experimental Augmented Reality (AR) prototypes which use see-through mode intended to be used for development purposes and short periods of time. 
Enabling and disabling see-through mode in experimental apps
- Press the Daydream button to open the Daydream Dashboard.
- Open the Settings menu by selecting the gear icon.
- Select Beta features.
- Toggle Turn on see-through mode to enable or disable see-through mode.
- Reboot the device.
Also, you can use the requestFeatures API
to request your users to enable see-through mode. For more information, download
the samples. For more information, see the getting guide for Android NDK
or Unity.