Eventually, biometrics might allow you to carry (or implant) nothing at all. A Swedish start-up called Quixter has outfitted stores at Lund University with a system that lets students pay by having the vein patterns in their hands scanned (vein patterns are less susceptible to fraud than fingerprints, since fingerprint dummies can deceive scanners). Iris scanners have potential, too—they’re hard to trick, and eyes, unlike hands, don’t change much with age, says Hector Hoyos, the founder of Hoyos Labs, which works on identity-authentication technologies. Hoyos thinks payments could one day be processed automatically—imagine your eyes being scanned as you enter an amusement park, the price of admission being deducted from your bank account as you get in line for your first ride.Of course, changes like these raise big privacy questions: if we pay for everything by phone or biometrics, companies will be able to track our movements and personal data to an unprecedented degree. Scott Rankin, the chief operating officer of Merchant Customer Exchange, the consortium behind CurrentC, says users will be able to alter their privacy settings to ensure that information about what they buy isn’t used or shared. But as Epstein, the computer scientist at SRI, points out, many people won’t mind sharing data if they believe they’re being compensated with good deals. “Most people are fundamentally lazy and will do whatever is easiest,” he told me. “What’s going to be easiest is not being anonymous.”

Gain Currency

Not so long ago, it looked as if we might be on our way to a single global currency, or two or three. European countries eagerly abandoned their national currencies in favor of the euro; in 2009, Zimbabwe began using other countries’ currencies in lieu of its own. Economically, these experiments haven’t worked out well, as the eurozone’s struggles suggest. And in fact, as digital technologies advance, shoppers are likely to use more currencies rather than fewer, says David Wolman, the author of The End of Money. From a merchant’s perspective, accepting digital pesos or rubles is less of a hassle—and less costly—than accepting foreign bills and coins.

As mobile technologies let stores track shoppers’ behavior more closely, customer-loyalty programs are likely to become more prominent, effectively creating new, private currencies, says Heather Schlegel, a futurist. Better data on buying habits will likely lead to more-targeted, and therefore more-enticing, offers. Stores might well begin to accept one another’s loyalty points: already, gamers can use Subway and Burger King gift cards to buy virtual goods for online games; down the road, you might be able to use, say, your Disney Dollars to pay for things at Walmart. Bitcoin, of course, is the most successful effort to create a decentralized “cryptocurrency”—a system of exchange that relies upon cryptography to validate and secure transactions, which are recorded in a public ledger. Whatever may come of it (so far, bitcoin’s value has been volatile), Bettina Warburg, a strategist for the nonprofit Institute for the Future, in Palo Alto, believes that some sort of successful “crypto-economy,” in which people can exchange goods without involving either banks or national currencies, is bound to develop. That could include more-widespread bartering of services, she says, perhaps with algorithms determining a deed’s value.