I just got excited about the iWatch. After all these months of rumor, hype, and over-analysis, it took just three little letters to make me see the light: NFC.

News reports today say Apple’s forthcoming smartwatch will have a Near Field Communication (NFC) chip inside, which could enable wrist-based mobile payments and lots of other things. It’s the set of secure functions enabled by the NFC chip that might justify the iWatch’s price tag, which some reports say could be as high as $400.

In a broader sense, most consumers associate smartwatches with fitness applications like step counters; the addition of mobile payments could get the message across that the devices aren’t just for the fitness minded.

But look at this from Apple’s point of view: It wants you to own at least an Apple laptop, an iPhone, and now a watch. Not just one product. All products. So the company must build functions into the watch that those other two devices — especially the phone, which will also have an NFC chip — can’t easily do. The NFC chip in the watch might be the key to this.

It’s not hard to imagine walking up to a retail counter and and touching your watch to a scanner to pay for something. If Apple does it right, this will be at most a two-step process: tapping the watch once, then moving your arm to put the watch in range of the scanner … that is, within 10 centimeters for an NFC connection.

That’s one of the reasons NFC is so commonly used for payments: the security is baked into the technology. The NFC radio fires off short bursts (around half a second, depending on the app) of data and will only work within a short range. Some has suggested that Bluetooth Low Energy could be used for secure transactions. But this technology, which has a bigger range and transmits more data, makes it far more likely that the data might be intercepted by people and machines that have no right to it.

So the iWatch needs use cases (beyond payments) where an authentication must be done within arm’s reach and where sensitive data is being exchanged. A few come immediately to mind. And some of them might even be in version one of the smartwatch:

Apple recently announced its Home Kit platform. One of the iWatch’s NFC functions might be opening the front door of your house with your watch. The authentication data being transmitted is indeed “sensitive” in that it controls access to many of the things you own or hold dear. Plus, it would also be easier than using the phone, as anyone coming home with bags of groceries can tell you.

The same logic might apply to your car. Apple might work with auto makers to enable a key-in system using the iWatch as the key. In that case, the watch would be held within range of the lock, and the NFC chips would exchange the authentification data.

For both house and car, the old physical keys would still work. Sometimes smartwatches run out of juice, I’m told.

The watch might also be used to check in for a flight at the airport. Sure you can do that with your phone, but how often does your phone’s auto lock turn on just as you’re about to swipe? And how many times does it change orientation at just the wrong moment? A swipe of the watch would be much easier.

In fact, the International Air Transport Association (IATA) just this year issued guidelines and standards that airports can use to set up NFC-based check-ins.

And scanning your watch to enter a public transportation system seems like a natural use.

In the health world, an iWatch (or some device like it) might eventually be the secure device we’ve been waiting for to carry our patient records around with us at all times.

One source points out that Apple would do well to pick out just a few of these killer uses for the watch and to make them work without having to tap the screen multiple times. Our phones are already multifunctional, and because of that, our directions must be more detailed and specific. We already swipe the phone to unlock, search for an app, launch the app, then use it. It’s simple, but not simple enough.

With a watch that performs just a small set of useful functions, the commands can be shorter and easier.

The sexiness or cool factor of the iWatch won’t sell the device in the numbers that Apple is hoping for. It will have to offer a few tricks that truly and obviously remove friction points from everyday life. And the NFC chip may be the key to those tricks.