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Source: Google.

Google (NASDAQ:GOOG) (NASDAQ:GOOGL) has brought Android Wear to iOS. Now, owners of Apple's (NASDAQ:AAPL) iPhones can take advantage of the wide variety of smartwatches offered by the search giant's many hardware partners.

The presence of Android Wear devices on Apple's platform might pose a competitive threat to the Apple Watch. Offered in many different styles and at many different price points, Android Wear watches could prove to be a compelling substitute.

But the company that seems more likely to be challenged is FitBit (NYSE:FIT). Given their lesser price tags, Android Wear watches could be enticing to potential FitBit owners.

Android Wear on iOS is extremely limited
New Android Wear watches, including the second-generation Moto 360 and the upcoming Huawei Watch, now support iOS -- at least, in a superficial sense.

In reality, Android Wear for iOS is heavily limited. It can show notifications from third-party apps installed on the user's iPhone, but it doesn't directly support them, nor does it offer as many watch faces as Android Wear for Android phones. Clicking on a link to a website from an Android Wear watch prompts that website to load in the Chrome browser on a paired Android phone. But if that watch is paired with an iPhone, it cannot access Chrome -- instead, it opens in a strange web viewer within the Android Wear app.

These shortcomings are far from surprising given that Google is working within the limitations of Apple's walled garden. In comparison, the Apple Watch offers greater functionality, including the ability to run third-party apps. Currently, Apple Watch apps are limited, but on September 16, Apple will update Apple Watch's operating system, giving it the ability to run third-party apps on the Watch itself. That should allow developers to offer even greater experiences to Apple Watch owners -- something Android Wear for iOS will not be able to match.

Google Now, notifications, and fitness
So, is Android Wear for iOS completely useless? Hardly.

In addition to seeing notifications, Android Wear owners can use Google Now, the search giant's digital personal assistant, and several native apps, including an app for the weather and Google Translate.

They can also take advantage of Google Fit, Google's fitness tracking app. All Android Wear watches include support for basic fitness-tracking features, like steps taken and calories burned. Most of them are equipped with a heart rate monitor, and some of them are waterproof. A few, like the upcoming Moto 360 Sport, even include built-in GPS for runners on the go.

That makes them strong alternatives to FitBit's dedicated fitness trackers. FitBit's mid-level offerings, the Charge ($129) and Charge HR ($149), offer similar fitness-related features (steps taken, heart rate), but lack support for Google Now and smartphone notifications. FitBit's flagship Surge does show notifications and includes GPS, but it retails for $249.

Android Wear watches are priced comparably, with most retailing for around $100 to $400. The program is just over a year old, but Google has already recruited nearly a dozen different companies to make Android Wear devices. Intense price competition should lead to even cheaper Android Wear watches over time.

iPhone owners now have another choice
Following FitBit's IPO, my colleague Evan Niu suggested that FitBit investors shouldn't worry too much about the Apple Watch. Given the wide disparity in pricing -- the Apple Watch starts at $349, and only goes up from there -- there's very little overlap between the two markets.

Android Wear, however, is an entirely different beast, and its expansion to iOS should give FitBit investors serious pause. Android Wear devices on iOS may not work as well as the Apple Watch, but they should work just as well as a FitBit. For the upstart wearable company, the competition could prove devastating.

Sam Mattera has no position in any stocks mentioned. The Motley Fool owns and recommends Apple, Google (A shares), and Google (C shares). 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.