Hardly a "well-placed hunch." Quoting from the decision:
"Shortly after his release from prison, a person who was a known user of meth reported to police that the defendant had brought meth to her and her husband, consumed it with them, and told them he wanted to start manufacturing meth again. Another person told the police that the defendant had bragged that he could manufacture meth in front of a police station without being caught. A store's security [*2] video system recorded the defendant buying ingredients used in making the drug. From someone else the police learned that the defendant was driving a borrowed Ford Tempo. They went looking for it and found it parked on a public street near where the defendant was staying. The police placed a GPS (global positioning system) "memory tracking unit" underneath the rear bumper of the Ford."
So they clearly had "reasonable suspicion." They probably also had "probable cause." If so they could have obtained a warrant.
The Court holds they didn't need a warrant because this wasn't a search. A cop can follow you when you're driving around - that's not a search. Earlier decisions have also held they can augment the "following" by placing a beeper in a container of chemicals defendant bought. They can even happen to be flying over your house and happen to see the pot plants you're growing.
Here the court says the GPS unit is just telling the cops where the car is being driven, which is really just augmenting what the cops would know if they followed him around themselves. Thus not a search.
I think it is a search, although it may be a reasonable one. At least reasonable suspicion should be required. To hold that it's not a search means the cops could randomly attach a gps unit to my car or yours, without any suspicion at all.
It would have been nice if the cops had gotten a warrant but assuming there wasn't time, the standard for reasonable should be articulable reasonable suspicion.