This morning, you left the house tagged with a tracking device that the government can use to find out where you have been and where you are going.
I'm talking, of course, about your cell phone...
While most courts considering the issue have held that police need "probable cause" to track your movements, a new decision (.pdf) last week out of the U.S. District Court of Massachusetts holds that law enforcement need show only "relevance to an ongoing investigation" to get a historical record of your past movement (something like the Jeffy trail in The Family Circus cartoon).
