13. The UPC, the most common version of the so-called bar code, wasn't as warmly embraced or as breathtaking as some emerging technologies, but its impact on retailing has been enormous. It saves $17 billion a year in inventory costs, by one estimate, not to mention carpal tunnel syndrome for countless cashiers. Other technologies, such as radio-frequency identification tags, may one day replace it, but the lowly UPC improved efficiency and supply-chain control almost invisibly. One of the few times it gained media notice at all was in 1992 when President George H.W. Bush marveled at it during a campaign visit to a grocers' convention in Florida. His reaction added to a perception that he was out of touch with the public, because many people were by then well acquainted with the technology. The rectangle of stripes and numbers has even fused its way into pop culture: In the former Fox television series "Dark Angel," Jessica Alba starred as a genetically altered fighting machine with a bar code branded on the back of her neck. Human bar-coding is thus far the stuff of science fiction, but the U.S. government uses the symbol in homeland security efforts, and airlines keep track of luggage with it. The Food and Drug Administration several months ago required a version of the bar code to be put on medications to cut errors.