>>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?

With the GPS you don't have to follow the person around though. To me it seems more like a bugging device - which *should* require a warrant.