Prosecutors justified this practice by saying it was no different from tailing or following a suspect. The Supreme Court disagreed, holding that
The Government’s attachment of the GPS device to the vehicle, and its use of that device to monitor the vehicle’s movements, constitutes a search under the Fourth Amendment.It's a welcome victory for privacy rights advocates. After the controversial passage of the NDAA on Dec. 31, civil libertarians must have been hoping for some good news.
How much tangible impact will this decision have on criminal investigations? Probably a very small one. Police departments will have to pay more overtime for old-fashioned surveillance on suspects, instead of using a fancy GPS unit.
Alternately, wireless technology and smart-phones have provided even better ways for law enforcement to establish location. As the BBC article on this case concludes,
...the ruling is unlikely to have an impact on the use by law enforcement agencies of another surveillance method, mobile phone tracking software.Police, and executive agencies with support of the Obama Administration, have had no trouble requesting location data from iPhone or iPad services to aid in criminal prosecution. I'm no legal expert, but this Supreme Court decision might establish precedent for that practice to be challenged in court as well.