One of the first really interesting uses of RFID (Radio Frequency ID) tags is described in this CNet article. A Japanese firm is looking at the possibility of using robots to guard playgrounds and other public spaces. It would be able to keep track of children by using RFID tags that would be worn by the kids, probably as a bracelet of some kind.
Anyone who entered the playground without a recognized RFID tag (teachers and parents would have tags) would be pursued by the robot, which could take pictures, flash lights, blow a siren, dial 911, chase the intruder, and even put out clouds of nontoxic smoke.
What also comes to mind after reading this article is developing robots that are able to use sensors to detect explosives, chemical/biological materials, and radiation, and deploy them in train stations, subways, airports, and other public spaces. We're in a war that is likely to last years longer, and we need to use technology creatively to defeat these terrorists and keep ourselves and our families safe.