Going into Apple's (NASDAQ:AAPL) event, the Apple rumor mill speculation related to the 4.7-inch iPhone 6 and the 5.5-inch iPhone 6 Plus was pretty much spot on. But there weren't any meaningful leaks about Apple's smartwatch before the event. That's why it is no surprise that when Apple unveiled what it is calling the Apple Watch, the device absolutely stole the show.

Apple Watch. Image source: Apple.

Starting at $349 and available in early 2015, this new Apple device is a game-changer for Apple stock. Here's why.

But first, here is a brief look at the new device.

What is the Apple Watch?
In somewhat of a surprising twist, Apple's newest technology takes serious cues from the classic watch designs we are used to. Further, Apple has given fashion a deserving nod by launching the device in range of different combinations of face collections and watch straps.

Apple watch. Image source: Apple.

But underneath the enclosures and wrist straps that maintain their sense of reverence for classic watches is some very impressive technology. As described in Apple's press release announcing the watch, here are some of the interesting features. 

Example of the Digital Touch communication on the Apple Watch. Image source: Apple.

  • Force Touch: senses the difference between a tap and a press.
  • A Digital Crown: the nob on the side that allows users to scroll, zoom, and navigate without obstructing the view on the display.
  • A Taptic Engine: Combined with a built-in speaker, this technology enables a "new vocabulary of alerts and notifications you can both hear and feel."
  • S1: A custom-designed system in package, or SiP, that has miniaturized an entire computer architecture onto a single chip.
  • Digital Touch: a new way of communicating by sharing sketches, taps on the wrist, recorded sound clips, or even your heartbeat.
  • Other hardware: an accelerometer, heart rate sensor, Bluetooth, and the ability to tap into an iPhone's GPS and Wi-Fi.

Importantly, the Apple Watch handles basic functions like text messages, phone calls, and mail as well. Paired with an iPhone, users can easily transition from a conversation or email on their wrist to their phone.

Of course there are still many questions about the device. For instance, how long does the battery last? How does Apple Pay, the tech giant's new mobile payment platform, work with the Apple Watch if the device doesn't have Touch ID?

But how well will the Apple Watch sell?
Isn't this the ultimate question investors are asking? No matter how interesting the Apple Watch is, it will only make a difference for Apple stock if a meaningful number of consumers are willing to open up their wallets (or scan their fingerprint with Apple Pay). But how well, exactly, will the Apple Watch have to sell to make Apple stock look enticing at $100 per share?

Consider this example scenario to get an idea of how the iWatch could impact Apple stock:

Assuming prices for the Apple Watch models range all the way from the starting price of $349 that Apple announced to $1,000 for the high-end models, and the average selling price for the device is around $500, 30 million units sold in the first year of availability would likely more than justify Apple's current stock price. This scenario would boost Apple's current annual revenue levels by about 8%.

Assuming the device sports margins comparable to the iPhone, this revenue could have an outsized positive impact on earnings -- perhaps in the range of nine to ten percent. Even more, 30 million Apple Watch sales in the first year of availability would suggest that Apple has tapped into a meaningful new growth market, providing further growth for Apple's revenue in years to come.

For perspective on what 30 million units could look like, consider that Apple has sold 164 million iPhones in the last 12 months and 70 million iPads during the same period.

Apple Watch. Image source: Apple.

With a bit of perspective and after seeing the Apple Watch, a forecast for 30 million Apple Watch unit sales doesn't seem farfetched. And if a scenario like this really does play out, investors may be underestimating Apple's potential in growing earnings over the long haul.

With a conservative price-to-earnings ratio of just 16, the new Apple Watch makes Apple stock a buy. After all, the iPhone 6 lineup alone serves as a meaningful catalyst for the stock; add-in the Apple Watch, and Apple stock looks like a good bet for the long haul even at $100.

Daniel Sparks owns shares of Apple and Tesla Motors. The Motley Fool recommends Apple and Tesla Motors. The Motley Fool owns shares of Apple and Tesla Motors. 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.