Tech's biggest companies are ramping up competition for the real estate between your hand and your elbow.

The big picture: The next big hardware platform after the smartphone will likely involve devices for your eyes, your ears and your wrists.

One big challenge for designers of this wearable computer of the future is where to put the central processor and the battery needed to power it.

Your forearm looks like the best candidate, right now.

Driving the news: Facebook is readying a competitor to Apple's Watch for release next summer, The Verge recently reported.

• Facebook's watch, per that report, will have a video camera on the front and will also be detachable, allowing users to deploy a second camera on the back.
• Facebook can also leverage big investments in VR hardware and a dominant consumer position with its Oculus Quest product line.
• Further down the road, Facebook researchers are exploring watch-like devices that will "virtualize" input by working with smart glasses to simulate keyboard and mouse data entry in AR.

State of play: Tech giants are rapidly staking claims to different pieces of the next-platform puzzle, involving different visions of the roles watches, earbuds and glasses or goggles will play.

Apple has a big lead in smart watches. So far it has tied the Apple Watch heavily to the health market. Apple's Watch depends on a linkage to an iPhone to work.

• Apple's wireless AirPods also have a strong market share.
• Apple has long been rumored to be hatching a smart glasses project, but the secretive company offers no clues to whether or when it might launch a product.
• Apple's prowess at integrating hardware and software could give it an edge. It could first tie all these peripherals together through the iPhone — then, later, figure out how to remove the phone from the equation.

Google's efforts to match Apple in the watch market with a competing operating system have largely stuttered.

• At this year's Google I/O, the company announced plans to merge its Android Wear platform with Samsung's Tizen-based watch ecosystem.
• The companytook an early shot at the glasses market with Google Glass, but that's now become chiefly an industrial product.
• The company's strongest wearables play is probably its acquisition of Fitbit, which brings a loyal following for its fitness oriented watches and trackers.

Snap, with its focus on cameras, has shown a determination to stake out turf in the AR glasses realm.

• Its latest products are available for AR developers but not yet for the public.

Microsoft has struggled in its efforts beyond the PC, having largely given up on mobile devices. It also had a very short-lived entry in the fitness wearable space, with Microsoft Band.

The bottom line: Right now this is a fight between Facebook, which wants to depend less on hardware providers in the post-smartphone era, and Apple, which aims to dominate whatever product category takes the iPhone's place. Google is down, but thanks to Fitbit, not necessarily out.

Why it matters: Hardware transitions only come every decade or two, and in the past they've given upstart contenders an opportunity to knock off the Goliaths who dominated the current generation.

Yes, but: So far, this time around, the Goliaths are fully in command of the field.