Ways of Watching: Recent advances in sensors and computing let governments, companies, and other institutions track people as never before. [1] One in four rental cars in the United States has a Global Positioning System tracking device, which allows companies to track the vehicle's movements in real time. [2] Foreign visitors to the United States now have their fingerprints scanned and photos taken at the border. [3, 4] Computer vision expert Mohan Trivedi's surveillance-camera system automatically blocks people's identities, rendering them instead as colored cubes. Should a camera detect suspicious behavior—a person running amid a crowd of walkers, say—the system automatically switches and reveals the person's true image. [5] To make sure students are lunching in the cafeteria, some schools in Pennsylvania have installed fingerprint scanners. [6] Cheap, disposable radio-frequency ID tags affixed to goods allow them—and you—to be tracked wirelessly.