The Quest solves this issue with what is being called a guardian system. Upon first putting on the headset in a new environment, users get to see a grayscale, low-resolution view of the real world, and are then being asked to map out their play space. After that first setup, a grid appears every time a user is in danger of leaving that play space when in VR. Go further, and the Quest switches back to the grayscale view of the real world. Take a step back, and you are back in VR.
That experience of the real world lurking just beyond the borders of your VR playspace is oddly fascinating. The Quest uses its integrated cameras for video pass-through, which explains why the images are as low-fidelity as they are. The cameras are primarily meant to track the controllers used with the headset, as well as the position of the headset itself in a 3D space, making it possible to lean into VR experiences, and reach out for virtual objects.
But even with those visual constraints, walking up to a Quest guardian and sticking your head through it feels like a profound transition from one world to another.
And while the Quest currently uses a guardian system to keep you safe in VR, future guardian systems may be outward-facing, and alert you that immersion is just a step away.