>http://www.wired.com/threatlevel/2010/09/public-privacy/#ixzz10GwocAiu

At first glance it seems like an invasion of privacy to do this without a warrant. But.................

You don't need a warrant to follow somebody and make a record of where s/he goes. Is it really so different to use a GPS device rather than a Mark I eyeball tracker?

Or should there be a warrant for both types of surveilance?