A pet missing for over a half year was found via the microchip implanted in its skin. The microchip was by HomeAgain, a company that is positioning itself as the third natural step for pet owners, after spaying /neutering and vaccination. According to the FAQ, the microchip is the size of a grain of rice. It's all very X-Files and Gothamist wonders when humans will start to be tagged.
Gothamist on animals with GPS tracking.