That little "entertaining" cell phone in your back pocket, which you are so addicted to thanks to all its apps, videos, messaging function and all other cool bells and whistles, that you can't possibly live without? It is simply the definitive NSA tracking beacon used to find where you are at any given moment.
http://www.zerohedge.com/news/2013-12-04/how-nsa-tracking-you-instant
http://www.zerohedge.com/news/2013-12-04/how-nsa-tracking-you-instant