New technology makes it possible to keep a much closer eye on people in public places. Cameras equipped with facial-recognition software can pick out known criminals in a crowd at airports, stadiums, and public plazas. Cars and cell phones equipped with location technology make it possible to track down people to within about 10 feet. Meanwhile, sophisticated X-ray machines that can see through people’s clothes may be more widely used at airports, government buildings, and even corporate lobbies. Many of these technologies have been stymied by privacy concerns in recent years, but now that fighting terrorism is the nation’s top priority, their use is expected to increase.