Every time a fourth grader passes through Rikkyo Elementary School's front gate, a small, gray plastic tag tucked inside his backpack beams a message to a computer in a nearby office.
The students are oblivious, but the computer logs the time they enter and leave, and a security guard watching the screen takes note. Moments later, their parents receive confirmation by e-mail.
High-tech tagging has made the jump from grocery stores to the schoolyard.