Too close for comfort?

          With GPS devices becoming more accurate and more prevalent in our daily lives it sometimes makes me wonder where the line should be drawn legally regarding their use.  Recently police put a GPS unit on a suspects vehicle without him being aware of it.  He was convicted and the judgment went in favor of it being legal to trace his movements in this manner.  Pineda-Moreno who was convicted will be taking his case to a higher court.  This case raises many questions.  Is your vehicle private property?  Did law enforcement breach his 4th amendment rights (no unreasonable search and seizures).  Arguments for both sides are made in this article pertaining to this case.
          The cost of GPS tracking units are really quite inexpensive.  I did quick search and I came across GPS tracking units for around a hundred and fifty dollars.  That's fairly inexpensive, as to where almost anyone could afford to own one.  It would not be unreasonalbe for parents to buy tracking devices for their young drivers cars without them knowing or police to track a violent fugitve; however, like many I am torn with the question of, "How far is too far?"
http://www.brickhousesecurity.com/gps-car-tracking-vehicle-logging.html