Homing Devices for Your Kids These days, panoptic vigilance is a much more practical matter, as the advent of kid-tracking technology for the consumer market shows. A company called Wherify Wireless in Redwood Shores, Calif., sells a satellite location device designed to be worn by young children. For $399 and a monthly service fee ranging from $25 to $50, parents can outfit their kids with a chunky plastic watch in ''cosmic purple'' or ''galactic blue'' that will transmit the wearer's location using signals from the Global Positioning System's network of satellites. Parents can retrieve the location on the Internet or by calling a Wherify operator.