David R. Humble was waiting in a grocery checkout line in a Florida supermarket 19 years ago when a moment struck him that may change the face of shopping. A customer ahead of him was so agitated by the cashier's inattention, he grabbed one of his items and swiped it over the scanner himself. The cashier got the message, Humble got a thought. Why not allow a customer to always do that? "It was so simple," he said. He returned to his job at a manufacturer of electronic security tags for clothing, toyed with prototypes and eventually formed CheckRobot Inc.