Sooner or later everything goes wireless. Over the decades we've figured out how to eliminate the cables that bring us sound, video, text, phone calls and data. Today there's only one major cable left to eliminate: the power cord.

Imagine if we could tap into power wirelessly! We'd all quit bellyaching about our phones being dead by dinnertime. Battery life would become a meaningless spec. A new era of gadgets could be thinner, sleeker, lighter and more flexible—because they wouldn't have to devote such a huge chunk of their volume to batteries.

And by “wireless charging,” I don't mean the lame idea of setting down your phone on a charging pad every night, as you can with some smartphones. That saves you plugging in a cord, but you can't use your phone while it's charging. No, we want to be able to keep our gadgets in our pockets, charging during the day. Charging through the air has been the holy grail for a handful of start-ups for nearly a decade—and an obsession of my own for two years. Several outfits, flush with venture-capital cash, are working hard on it, presenting demos and getting observers excited. Wireless charging would be popular, profitable and transformative. So what's the holdup?

To start with, most of these technologies work by transmitting RF (radio-frequency) waves. Our future phones, tablets, laptops, watches and Fitbits will have to be equipped with compatible receivers that convert these Wi-Fi-like waves back into power.

That, for example, is how Powercast's technology works. Since 2010 this company has been selling industrial products, such as equipment sensors and active RFID tags, that can recharge at a distance. It hopes to get into consumer products soon.

Unfortunately, Powercast's technology transmits only microwatts or milliwatts (millionths or thousandths of a watt), which is nowhere close to enough for charging a phone. Even worse, it can't track your gadget's position in the room; you have to leave the device in a predefined spot. Charles Greene, chief operating officer, says that he imagines that you'll set your phone down on the bedside table every night.

Well, cool. But not what the world is hoping for.

Companies such as Ossia and Energous have a more ambitious plan. Their transmitters contain an array of hundreds of antennas, which pinpoint your device as you move around. Now that's more like it, right?

Well, yes. Yet here again, the dream of phones charging in our pockets is elusive. Energous marketing officer Gordon Bell says his products will trickle-charge your phone through the air—when it's in your pocket. But if you're using the phone during the day, the best you can hope for is that the transmitter will keep the battery level from going down.

Then there's uBeam, which uses ultrasonic waves to transmit power. Unfortunately, this technology requires line of sight to the transmitter—so you have to hold your body in the same position all day. (Furthermore, uBeam's former vice president of engineering now says the technology will never work.)

And there's the Federal Communications Commission problem. You can't sell wireless tech in the U.S. until the FCC has concluded that it's safe and doesn't interfere with existing wireless products. At the moment, the agency permits wireless transmission in two categories: very low power at a distance (such as Wi-Fi) or higher power that is contained or localized (such as microwaves or charging pads). Clearly, neither category currently permits long-range, higher-power transmission.

Energous asserts that its power transmission is, in effect, localized, thanks to that beam-forming array. If the FCC buys that argument, then it and its rivals might have a shot at bringing their products to market.

The company says that it expects to have FCC approval of its first through-the-air charger, a desktop model with a three-foot range, by the end of this year. If that comes to pass and if the world's makers of consumer products take the bait, then we may be in luck. Maybe 2018 will be the year the last wire went away.