As Apple's (NASDAQ:AAPL) Tuesday event approaches, buzz about the tech giant's plans for the keynote is hitting an all-time high. But no matter how active the Apple rumor mill is going into the event, Apple's continued emphasis on secrecy has proven to pay off exceptionally well this year, leaving its impatient followers in a desperate wonder. Sure, it is clear that Apple is likely to launch two versions of the iPhone 6 and a wearable device -- but there are some other potential products that may be released and a few rumored features for its new devices that are still raising eyebrows. Here are the three biggest question marks headed into the event.

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Alleged leaked 4.7-inch iPhone 6 rear casing. The part was first shared by Feld & Volk.

What is one-handed mode?
Apple's unwillingness to transition to smartphones with larger displays as rapidly as other manufacturers have may have been partly due to the company's uneasiness about a user experience that could require two hands for typing, according to The New York Times. But, the Times reports that Apple has an interesting solution.

To deal with concerns that a bigger phone will make typing with one hand difficult (the current iPhone has a 4-inch screen), some changes to the design of the iPhones' software interface will allow people to type or use apps with just one hand -- there will be a one-handed mode that can be switched on and off, two employees said.

Apple's iPhone 6 models will allegedly come in two different screen sizes: 4.7-inches and 5.5-inches. These are both larger than Apple's 4-inch iPhone 5, 5c, and 5s. One handed mode could serve as a partial explanation for why Apple is only now releasing phones with larger displays.

NFC? Really?
It's been rumored for quite some time that Apple wants to launch a mobile payments service. But the question has always been: What technology will Apple use for the service? Speculation headed into tomorrow's event points to Apple finally adopting near-field communication technology in its iPhone 6. In fact, the Times even asserts that NFC technology will be built in the iWatch, too.

NFC technology isn't new. Apple could have adopted it long ago. Sure, it may not have been as useful before Touch ID, but if Apple really believed in NFC, the company could have built it into the iPhone 5s -- Apple's first phone with fingerprint scanning technology. But since NFC technology requires retailers to upgrade their point-of-sale systems to include the technology, it still seems questionable that Apple would require NFC for a mobile payments service.

Touch Id 

Touch ID demonstration on iPhone 5s. Apple's Touch ID is likely to be a foundational building block for Apple's payment service. Image source: Apple.

But longtime Motley Fool Apple analyst Evan Niu suggests the question is no longer whether or not the technology will be used in the phone. The better question, he says, is whether or not Apple will require NFC technology for its mobile payments service or simply support it. Allowing for other technologies in addition to NFC in order to conduct transactions could broaden adoption of the payments service.

Obviously the broader the appeal for Apple's new mobile payments service, the better for investors -- as long as any other technologies Apple decides to support in addition to NFC are equally as effective.

It's time for an Apple TV refresh, right?
The last time Apple refreshed its Apple TV was March 2012. Sure, the company has added plenty of channels since then and provided a few major software updates. But the hardware is undoubtedly due for an upgrade. In fact, even the software is starting to appear outdated.

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Could we finally see an update at Tuesday's event? Unfortunately, probably not. There isn't any concrete evidence that Apple will refresh the device. Still, the device's age alone makes a refresh at least possible -- though very unlikely.

How about at least a software development kit for Apple TV that will finally allow third-party developers to build apps, Apple?

Investors will be watching these three items closely. A one-handed feature and an effective mobile payments service would both serve to boost the value proposition for Apple's new iPhone and a new Apple TV would strengthen the company's ecosystem.

Daniel Sparks owns shares of Apple. The Motley Fool recommends Apple. The Motley Fool owns shares of Apple. 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.