...next time you go to a protest.  A couple months ago while waiting in line somewhere, I was playing with my cell phone and noticed a GPS function of sorts which would allow my phone to be located by satellite.  Since I don't use GPS through my phone, I decided that was a little weird and turned the function off. 

According to a recent post on the Cato@Liberty blog, that may have only been so effective:  all mobile devices can be tracked within 60 to less than 10 meters, depending on what kind of capabilities your phone has enabled.  If government gets its hands on this data, it could be used not only to predict your location at any given time based on your past movements, but also to seriously limit free speech:

A government not so keen on free speech could use such data to see a crowd converging towards a protest site and respond before the swarm takes form — detected and preempted, this protest never happens. Or worse, it could be used to understand and then undermine any political opponent.

Concerning, no?  Read the rest here.