Single player apps must pause when the user removes the headset or opens the Universal Menu.
Note: Not required for multiplayer apps.
In Unity, you should see
OnApplicationPause(true) called both when the HMD sleeps after dismount, as well as when the display is turned off from the power button.
This will be matched by a corresponding
OnApplicationPause(false) when the headset is remounted, or the power button is hit again to turn on the display.
Things that cause
OnApplicationPause(true) to occur:
App should pause or react within the amount of time configured under Settings > Power > Auto Sleep on the HMD.