As the old saying goes, a smile costs nothing but gives so much. In the future, it will offer a lot more, including everything from the ability to fly across the country to the means to purchase fried chicken.

If you live in China, the latter is a present-day reality. The Alibaba-owned Alipay, a mobile app used by 120 million people in China, lets you transfer money using facial recognition as a verifier. In early September, Alibaba's Ant Financial unit also launched face-based payment with KFC.

For Chinese consumers, this means that they can leave their wallets and their smartphones at home. Of course, it also means that the government has a means to track their identities. But would face-based payment fly in the U.S.? The possibility is stronger than you might think. Here's why…

1. Facial recognition has gotten really good

Thanks to deep learning, facial recognition has improved significantly in just the past few years. In January, Baidu used its facial recognition technology to create a TV show in China. The show puts AI to the test by challenging its face and voice recognition capabilities against human competitors who claim to be adept at recognizing face and voice characteristics in other humans. So far, Baidu's system has a solid track record of defeating its human competitors on the show.

Facial recognition technology can now identify faces even if the lighting is poor or the view is from an odd angle. In China, the technology has gone from a curiosity to a regularly employed technology. Even some banks in the country use facial recognition to grant loans, and citizens in China can board trains and pay for their tickets by showing their faces instead of the contents of their wallets.

2. Apple, Facebook, Google, and Amazon are on board

Apple's iPhone X will feature Face ID technology that lets users unlock their phones with their faces. Apple has taken steps to assure consumers that it won't store images of their faces in the cloud. Facebook's position, meanwhile, isn't as clear — the company is using its massive database of consumer images for its AI research and may ultimately use facial recognition to learn about users' hobbies, preferences, and interests for targeted advertising. Google also uses facial recognition in its Android platform and may be preparing for a way to share facial recognition data so that your face will immediately be tagged in your friends' photos, a feature that Facebook already employs. And while Amazon doesn't have a public-facing use for its facial recognition yet, the company has a robust facial recognition program.

3. It will offer huge convenience

Imagine walking into a store, grabbing what you need, then flashing a smile at a camera to pay. Things like grabbing a coffee at Starbucks and boarding the subway would also be this seamless. In this future world, your phone won't be as important. In fact, with a smartwatch, you will be able to do most of what you need to do without a phone, by using Apple Pay or Samsung Pay. Your phone will likely become what your laptop is today — a piece of hardware you use to get work done.

OK, now the obvious downside: A facial recognition database is the stuff of dystopian sci-fi. Forget about your privacy — if the government and the top tech companies can identify you anywhere, then wherever you go, you'll leave a data trail.

The catch is this is already happening to an extent. Smartphone data is already being used as evidence of cheating in divorce trials. Amazon has handed over data from its Echo device for use in a murder trial. Consumers in the near future will have to grapple with the fact that Echo is always listening and their iPhone is always watching.

The question then is how much privacy consumers are willing to trade for convenience. In the U.S. at least, the answer is probably a lot. That's why China soon won't be the only country where you can use your face to go shopping.

Lexi Golden is an accounts manager at Glassview, a marketplace for brands and publishers.