Apple (NASDAQ:AAPL) announced two brand-new products at its big event on Tuesday (three, if you count the new U2 album). The Apple Watch and Apple Pay are both exciting for investors because they have strong potential to draw Apple users -- or soon-to-be converts -- deeper into the company's ecosystem.

The Apple Watch works with the iPhone, the iPhone works with Apple Pay, and Apple Pay works with the Apple Watch. I'd imagine Apple Pay will also work with the new iPads -- acting as point-of-sale systems -- once those are released.

Apple Pay uses Touch ID on the new iPhones to authenticate a user and access his or her credit card data. In Tuesday's announcement, Apple said Watch will also work with Pay, but gave no details on how exactly that will work considering that the device has no fingerprint scanner.

Apple might have figured out a clever solution that has even less friction than scanning fingerprints. It could use a heartbeat to authenticate a user.

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With a simple wave of the hand ... Source: Apple Keynote Replay.

In the works for months
Last December, Apple filed a patent for a "seamlessly embedded heart rate monitor." Within that patent, Apple stated that an "electronic device can authenticate a user based on the attributes of the user's heartbeat. For example, the durations of particular portions of a user's heart rhythm, or the relative size of peaks of a user's electrocardiogram (EKG) can be processed and compared to a stored profile to authenticate a user of the device."

Apple isn't the only one onto this. In 2012, researchers at National Chung Hsing University in Taichung, Taiwan, headed by Chun Liang-Lin used electrocardiographs to extract the unique mathematical features underlying each person's heartbeat. The group created a proof of concept by using the heartbeat to generate a key that could later be used to decrypt sensitive information.

The Apple Watch comes with four sensors on its back that sit on the skin and use light beams to sense a user's heartbeat. Apple showed off the sensors with a function that allows you to send your heartbeat to a friend, giving that person haptic -- or "taptic" -- feedback on his watch. It's just a gimmicky little function. Of course, the heart rate sensors also play a large part in the device's fitness apps.

Perhaps, however, the gimmicky heartbeat feature is just an example of how developers can use and access a person's heartbeat for use in their own apps -- even for use in authentication. It could be the killer application smart watches need to move into the mainstream.

Frictionless interactions
Apple Pay is the prime example of how heartbeat authentication could completely reduce the friction of transactions. Even in the example of the iPhone using Apple Pay, a user has to scan his or her thumbprint via Touch ID. With heartbeat authentication, the only thing a user would need to do is hold a wrist close to the near field communication receiver. It doesn't get much easier than that. It solves the problem of having to get something out of your pocket or purse. (As sarcastic as that sounds, I'm actually serious.) 

But the authentication feature could go beyond payments. In the keynote, Apple showed off an app from BMW that will remember where you parked and give you directions back to your vehicle. Imagine if the app also unlocked your car when you grabbed the door handle and started it up when you grabbed the wheel (but after you buckled up). 

Android Wear features Google Now, which brings up information based on context. For example, it will get your digital boarding pass as you run through the airport to catch your plane. What if you never needed to call up the boarding pass? Apple Watch can authenticate your identity and match it with the airline's system instantly, and then bring up your assigned seat on the display.

Starwood Hotels & Resorts offers another good example of the possibilities. Its app will unlock your hotel room door. It's not unlikely someone will create an app to unlock your home door. (Hold on, let me submit this patent really quick.)

Better than using an iPhone
These things are all possible with the new iPhones, but requiring a person to take his or her phone out to unlock something is more friction than using a key. With a device already strapped on the wrist, it's frictionless.

People's main complaint about smart watches is that they don't do anything you can't already do with the smartphone in your pocket. The same is true of the iPad, though. Pretty much everything available on the iPad is available on the iPhone. The reason the iPad sells is that it does certain things better -- like watching Apple keynotes.

Frictionless authentication -- to make payments, to unlock doors, and to do things nobody's yet imagined -- is what the Apple Watch could do better than the iPhone.

Adam Levy 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.