When Patrick McMullan wants a Diet Dr Pepper while he's at work, he pays for it with a wave of his hand. McMullan has a microchip implanted between his thumb and forefinger, and the vending machine immediately deducts money from his account. At his office, he's one of dozens of employees who have been doing likewise for a year now.

McMullan is the president of Three Square Market, a technology company that provides self-service mini-markets to hospitals, hotels, and company break rooms. Last August, he became one of roughly 50 employees at its headquarters in River Falls, Wisconsin, who volunteered to have a chip injected into their hand.