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Another way to track objects is through radio-frequency identification tags, like those used to monitor livestock. These “e-tags” range in size from a grain of rice to a quarter and so can conceivably be embedded in everyday objects. Most rely on inductive coupling, like that used in the bulkier tags placed on clothes to deter shoplifting. Unlike bats, e-tags have no internal power source that needs periodic replacement. Instead, a signal from a tag reader induces a current in the implant, which consists of a coil attached to a silicon chip. Energy captured by the coil is stored in a capacitor that powers the chip and causes it to transmit a unique identifier to the reader. From there, the data is relayed wirelessly to the Internet or company intranet–summoning more information relating to the tagged item.

Last year, PARC researchers e-tagged everything from paper to books to copier machines around the lab. That way, anyone carrying a tablet computer equipped with a reader could access additional information and services associated with the tagged item. Say, for example, a person approached a flyer announcing a lecture. By positioning the computer near the title, he or she could call up the talk abstract. Holding it near the date and time announcement, where a separate tag was embedded, would schedule the event in an electronic calendar. Even better, many tagged items activated services associated with their physical form. In one demonstration, bringing a tagged French dictionary near a computer summoned a French version of the English document then on the screen. Roy Want, who led the project but has since left Xerox for Intel, describes e-tags as “an evolution of the bar code. I think in the future almost anything that is manufactured and traded will contain an electronic tag.” Such tags, he adds, will link to the Internet to provide information about the item’s origin, history and ownership.

Although a world populated by bats and e-tags promises to extend computing to almost anything, it does not address one of the biggest hopes for ubiquitous computing-that sensors, effectors and actuators can also be incorporated into devices, making systems capable of both processing information and responding to it. Former PARC director John Seely Brown, for example, foresees a world where millions of networked sensors are placed in roadways, using information about traffic to ease congestion and thereby “harmonize human activity with the environment.”

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