Handles pausing and resuming for the Oculus platform.

WorldSettings.cs

using System.IO;
using UnityEngine;
using UnityEngine.Events;
#if PLATFORM_ANDROID
using UnityEngine.Android;
#endif

public class WorldSettings : MonoBehaviour
{
    /// <summary>
    /// Events to be called when when the game is paused or resumed.
    /// </summary>
    public UnityEvent PauseEvents, ResumeEvents;

    /// <summary>
    /// Indicates whether the game is paused or not.
    /// </summary>
    public static bool IsPaused
    {
        get
        {
            return OVRManager.hasInputFocus;
        }
    }

    /// <summary>
    /// The events that have occured so far. Helps ensure that if the inputs are lost and the HMD unmounted, then
    /// we pause this as expected.
    /// </summary>
    private int mEventStack = 0;

    #region Unity overrides.
    private void OnEnable()
    {
        OVRManager.HMDMounted += OVRManager_HMDMounted;
        OVRManager.HMDUnmounted += OVRManager_HMDUnmounted;
        OVRManager.InputFocusAcquired += OVRManager_InputFocusAcquired;
        OVRManager.InputFocusLost += OVRManager_InputFocusLost;
#if PLATFORM_ANDROID
        VerifyPermission(Permission.Microphone);
        VerifyPermission(Permission.ExternalStorageRead);
        VerifyPermission(Permission.ExternalStorageWrite);
#endif
    }

    private void OnDisable()
    {
        OVRManager.HMDMounted -= OVRManager_HMDMounted;
        OVRManager.HMDUnmounted -= OVRManager_HMDUnmounted;
        OVRManager.InputFocusAcquired -= OVRManager_InputFocusAcquired;
        OVRManager.InputFocusLost -= OVRManager_InputFocusLost;
    }
    #endregion

    #region Helper methods.
#if PLATFORM_ANDROID
    private void VerifyPermission(string permission)
    {
        if (!Permission.HasUserAuthorizedPermission(permission))
        {
            Permission.RequestUserPermission(permission);
        }
    }
#endif

    private void pushEventStack()
    {
        mEventStack++;
        if (mEventStack > 0 && Time.timeScale != 0.0f)
        {
            Time.timeScale = 0.0f;
            PauseEvents.Invoke();
        }
    }
    private void popEventStack()
    {
        mEventStack--;
        mEventStack = Mathf.Max(mEventStack, 0);
        if (mEventStack <= 0 && Time.timeScale == 0.0f)
        {
            Time.timeScale = 1.0f;
            ResumeEvents.Invoke();
        }
    }
    #endregion

    #region Event definitions.
    private void OVRManager_HMDUnmounted()
    {
        pushEventStack();
    }
    private void OVRManager_HMDMounted()
    {
        popEventStack();
    }

    private void OVRManager_InputFocusLost()
    {
        pushEventStack();
    }
    private void OVRManager_InputFocusAcquired()
    {
        popEventStack();
    }
    #endregion
}

Modified to include checking for HMDMount and unmount.

 OVRManager.HMDUnmounted += OVRManager_HMDUnmounted;
OVRManager.HMDMounted += OVRManager_HMDMounted;

 private void OVRManager_HMDUnmounted()
    {
        AudioListener.volume = 0f;
        Time.timeScale = 0.0f;
    }

    private void OVRManager_HMDMounted()
    {
        if (IsPaused) return;
            AudioListener.volume = 1f;
            Time.timeScale = 1.0f;
    }