This article was updated on April 1, 2015.

Check out Steve's Aug. 8, 2015, article updating his look at these three stocks: "3 Tech Stocks to Buy Now That We're After the Apple Watch Launch"

With shipments of Apple's (NASDAQ:AAPL) long-awaited Apple Watch set to begin on April 24, 2015,  excitement surrounding the new device has reached a fever pitch.

It's unclear exactly how many units Apple might sell, but early reports say the tech giant wants to ship as many as 3 million Apple Watches per month to start. With models ranging in price from $349 up to $17,000 -- and no, that's not a typo -- Apple Watch represents a huge opportunity for the company to not only gain incremental revenue, but also make its existing ecosystem of products that much stickier for consumers.

Buying shares of Apple isn't the only way investors can play the device. Here are three companies making products that are likely crucial to the iWatch's unique functionality.

On Apple Watch's curved, flexible display
First up is OLED technologist Universal Display (NASDAQ:OLED)

Early last year, LG Display was rumored to have signed an exclusive agreement with Apple to provide millions of small, flexible OLED displays for the Apple Watch. It's unsurprising that agreement hasn't been officially confirmed yet given Apple's secrecy. But assuming Apple Watch's display is indeed OLED, none of this would be possible without Universal Display, which licenses its OLED patents and sells OLED material to LG Display.

There is one caveat: The small screen size involved in producing Apple Watch displays won't do much to boost Universal Display's material sales volumes. But as I wrote when the initial deal with LG Display was reported, "Merely having Apple acknowledge [...] Universal Display's flagship technology should go a long way toward convincing skeptics of its long-term viability."

Sure enough, more recent rumors suggest Apple has tasked suppliers Innolux and Foxconn with building a massive new factory dedicated to producing flexible OLED displays for both wearable devices and a larger smartphone -- the latter of which indicates OLED could be coming to future iPhone models. If that sounds ambitious, keep in mindSamsung has also confirmed plans to offer devices with foldable OLED displays by the end of 2015. Both cases portend great things for Universal Display shareholders.

On Apple Watch's motion sensors
Next, what's an Apple Watch without cutting-edge motion sensors? And that's where motion chip specialist InvenSense (NYSE:INVN) comes into play.

Luckily for investors, shares of InvenSense are still reeling after a series of disappointing earnings reports in part thank to heavy investments in research and development. But according to InvenSense CEO Behrooz Abdi, that R&D opened up "exciting business opportunities in emerging applications, such as wearables" [emphasis mine].

As development costs stabilize in the coming quarters, I think InvenSense shareholders will be more than happy they held on.

On the Apple Watch's protective cover
Finally, consider high-tech glass specialist  Corning (NYSE:GLW) as a play on Apple Watch's durable glass display cover.

And yes, I'm aware two of the three Apple Watch Models -- the standard "Watch" and "Watch Edition" versions -- will boast highly scratch-resistant sapphire crystal covers when they begin shipping. And Corning doesn't currently produce sapphire, which it argues doesn't fare as well as its own Gorilla Glass when dropped. Keep in mind, however, Apple was forced to find alternate sources for sapphire after the shocking bankruptcy of sapphire supplier GT Advanced Technologies last October. 

What's more, given the fact Gorilla Glass has long served as the protective cover of choice for Apple's iPhones, it's highly likely Corning is the company behind the "strengthened Ion-X glass" featured on the Apple Watch "Sport" model. That also happens to be the leastexpensive of the three models, so is most likely to sell in higher volumes.

If that's not enough, Corning management recently told investors they will soon commercialize a new product with the same damage resistance as Gorilla Glass, but with scratch resistance "approaching sapphire." As a result, I won't be the least bit surprised if Corning eventually wins a spot in all three Apple Watch models while continuing to protect Apple's massively popular iPhones. If that happens, patient Corning investors will be the ones who reap the rewards.

The next billion-dollar Apple secret
Apple forgot to show you something at its recent event, but a few Wall Street analysts and the Fool didn't miss a beat: There's a small company that's powering Apple's brand-new gadgets and the coming revolution in technology. And its stock price has nearly unlimited room to run for early-in-the-know investors! To be one of them, just click here.

Steve Symington owns shares of Apple, InvenSense, and Universal Display. The Motley Fool recommends Apple, Corning, InvenSense, and Universal Display. The Motley Fool owns shares of Apple, InvenSense, and Universal Display. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.

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