Google’s virtual-reality headset efforts are clearly gathering pace — last month it established a fully-fledged VR division, and less than a week ago it was reported to be working on a plastic successor to its bestselling Cardboard headset, which uses smartphones for the display and processing power.

But here’s a new twist in the rapidly unfolding tale. According to the Wall Street Journal, Google goog is also working on a standalone virtual-reality headset that does not rely on other equipment.

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All the other VR headsets that are on the market or soon to enter it, from rivals such as Samsung, Facebook’s fb Oculus, HTC and Sony sne , rely on smartphones, PCs or games consoles for their functionality.

According to the report, the new headset will have its own screen as well as outward-facing cameras that track the user’s head motions. The Journal‘s sources seem divided on whether the device will hit shelves this year or — as it’s still in early development — possibly not see a release at all.

In some ways, the idea of a standalone VR headset makes a lot of sense. Staring at a smartphone at very close proximity can cause headaches that specially designed screens are less likely to trigger. A device will also generally be an easier sell if you don’t have to have other expensive gear to make it work (depending, of course, on the cost of the device itself — Cardboard cost as little as $19 and sold 5 million units).

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However, the big question is how good the battery life will be.

There’s a reason this year’s crop of VR devices tend to be companions to other computers — it means they get to offload the heavy processing associated with high-resolution imagery that must constantly update to take account of the user’s head movements. Processing sucks power, as does a screen that remains on as long as the user is wearing the headset.

If Google is going to release this thing, it will need to strike a very careful balance between brawn and power efficiency.

Still, with Cardboard having already encouraged people to try out VR apps and view VR videos on YouTube, the new device may be well-timed to tap into a growing market that features established content.