The ATF has announced that it has adapted the technology that allows a small tattoo to monitor, for example, blood sugar in diabetics, to make tattoos RFID traceable across wide geographical areas. The addition of the tracing compounds to the tattoo ink will make it harder for the agency to misplace its informants, the bigger the tattoo, the wider the range. An informant with full-body tattoos will be satellite traceable anywhere in the country. Research is continuing to add flexible circuitry to the ink to make an informant a permanently wired infiltrator without the bulky and easily detectable boxes associated with the current "wires".
Update: Sorry this was late. Should have been up yesterday.