AR glasses are what comes after the smartphone

How it works: Such glasses allow users to see what's in front of them, but with digital information overlaid, such as map directions, contact information and messages. Cameras and microphones enable capturing images and sounds and allow for different types of input, with speech likely to play a key role.

Who is involved: Apple, Google, Facebook and Microsoft have all shown an interest and invested heavily in the underlying technologies. Analysts also expect phone makers like Samsung and PC makers like Lenovo to get in on the act.

Be smart: If you look closely, you can see some of the key underlying technologies already being developed and tested in plain sight.

• Facebook plans to debut smart glasses later this year, designed in partnership with Ray-Ban maker Luxottica. These glasses — a more advanced twist on the niche spectacles Snap has been selling — are unlikely to offer full capabilities, but rather serve as a stepping stone, both in terms of technology and helping people get used to such devices in their lives.
• Facebook's Oculus unit has been focusing mostly on virtual rather than augmented reality, but there is a fair amount of crossover between the two. The Oculus Quest 2 and other VR headsets can deliver AR by using cameras to see into the external world.

• Microsoft already sells Hololens, which packs the power of a Windows 10 computer into a headset, albeit one that is still too bulky and expensive to appeal to consumers. Microsoft has made it available to developers and some enterprise customers, and is also doing early work with the U.S. Army.
• Google Glass, the first device in this category that attracted mainstream attention, flopped as a consumer product, but a slightly updated version is still being sold to businesses.
• Apple has shared few specifics, but has been making lots of moves — including a recent move of executive Dan Riccio, reportedly to head Apple's VR/AR efforts. According to reports from Bloomberg and The Information, Apple is readying a VR headset that would also use cameras to see into the real world. The device, which may cost in the range of $3,000 and arrive next year, could serve as a chance for both high-end consumers and developers to start testing the technology that would make fully developed AR glasses work.
• Both Apple's AirPods and Apple Watch represent efforts toward miniaturization of the technology and ways to test individual components, such as the spatial audio feature included with the latest AirPods Pro. Several companies hope to solve some of AR glasses' tough technical challenges by splitting the computing work among multiple devices. Qualcomm, among others, aims to offload some of the glasses' processing needs onto users' smartphones .
• Pokemon Go creator Niantic has a partnership with Qualcomm and has also been busy mapping the real world and developing the kinds of augmented reality experiences that consumers will want.

Yes, but: The technical hurdles are many, especially if the goal is really something as light and inconspicuous as eyeglasses.

• Miniaturization: While many of the computing pieces are in place for such glasses, including tiny cameras, microphones and processors, the components aren't all yet small enough to have something that is both full featured and lightweight.
• Battery life: Just like you want your smartphone to last all day, you'd like to be able to have your smart glasses work wherever you go. Many of today's headsets, both VR and AR, last only a couple of hours between charges.

• Heat: Today's processor chips are more energy efficient than ever, but they still give off heat when they're working hard, and users aren't going to appreciate that when the device is resting on their face.
• Display: Many of today's AR glasses have only a limited field-of-view, rather than the ideal experience of being able to place computing imagery anywhere the eye can see. Devices also have a hard time providing a bright enough light source to make their projected information easily viewable in sunlight.
• Cost: Putting all the needed technology in a single device, even with the above limitations, adds up to a product that costs several thousand dollars.

"The challenge is to make the technology more power-efficient so it can be worn for a longer period of time, without impacting the form factor," Qualcomm VP Hugo Swart told Axios. "AR glasses need to become smaller, lighter weight and have longer battery life. Qualcomm is committed to making AR glasses the next big thing,"

Even harder than the technical challenges are the new technology's social dilemmas, Facebook Reality Labs head Andrew Bosworth told Axios.

"How do you fit this all into a socially acceptable, comfortable form factor that people feel fits the way they want to express themselves? And then of course you have to consider the people who don’t have the glasses. How does this impact them, how do you solve for their discomfort? How do you bridge the privacy concerns with always on cameras and microphones?"

That's part of why Facebook has launched Project Aria, an effort to measure the societal reaction to smart glasses that have always-on cameras and microphones.

Our thought bubble: Even if users can be persuaded to trust that their glasses aren't spying on their friends and families or recording their private conversations, the new devices will demand new norms for every conceivable social situation.

Flashback: These questions came up back when Google first introduced Project Glass back in 2012.

• Part of what doomed the pioneering smart glasses as a consumer wearable — beyond the immature technology — was that they were widely viewed as creepy and intrusive. (Remember this?)