RFID

The world's smallest radio frequency identification tags have been unveiled by Japanese electronics firm Hitachi. The minute devices measure just 0.05mm by 0.05mm (0.002x0.002in) and to the naked eye look like spots of powder. They are thin enough to be embedded in a sheet of paper. Read more and more.

Apparently the smallest RFID antenna is about 4mm, so one wonders if such extreme miniaturization is really necessary.

Now any tiny piece of thin wire you find on your clothing could in theory be a functional RFID tag... Should we be worried about our privacy? A commenter on Bruce Schneier's blog offers this solution against being tracked: