Most people are aware that they are absolutely surrounded and saturated by RF. Its hard to imagine that you're swimming in it, but you are. Unless of course you've built a Farraday cage around your home... I'll tell you how to do that sometime. this time I am not talking about spectrum saturation. i am talking abotu the little tiny transmitters you are taking home from Walmart. They (and many other big box stores) use RFID chips. They cost 7.2cents to make, and tahat's why there are so many of them.
An RFID chip stores and allows for the remotely retrieval of ID data. It can be attached to or imbedded into any product and even into a person. Libraries, schools, our government, and big businesses are all adopting (RFID) radio frequency identification tags. The device can be quite small: commercially available products exist that can be embedded under the skin. The smallest one I am aware of measures 0.4 mm × 0.4 mm, and is thinner than a sheet of paper. It's a little chip that can pinpoint the location of anything you stick the tag to. While RFIDs are a convenient way to track say the xmas present the post office lost... Its also an easy way to track people and what they do. RFID chips could be used to track you and all your belongings, effectively profiling you thru your shopping habits. ...and things even less benign.
In 1945 Léon Theremin [yes he invented the theremin too] invented a passive covert listening device, for the soviet government. it was not exactly an identification tag, but it is generally attributed as the "first known" RFID device. It was called "the great Seal" bug. His bug, unlike previous bugs, used inducted energy from radio waves of one frequency to transmit an audio signal on another. This made the device hard to detect since it did not radiate any signals unless it was actively being powered and listened to remotely. This feature also endowed it with potentially an unlimited operational life. Iit's name came from an incident whererin a bug of this nature was embedded in a wooden plaque and presented to the American ambassador in Moscow by Russian schoolchildren. It hung in his office until detected by a professional bug sweeper months later. [It was a fine moment in the annals of spooks everywhere.]
FYI: How to kill the little buggers:
RAID KILLS BUGS