The fact that the lower court never considered the reasonableness of the search and whether the automobile exception to the warrant requirement was applicable makes United States v. Jones an interesting but relatively unimportant decision.

Imagine the same facts, same case, except the lower court did make a ruling as to whether the automobile exception applied. Then, the Court would have to either say that the "search" was of the person, or invent a new exception to the exception, i.e., a protection against GPS surveillance of a car.

Attorneyparedes.wordpress.com

Re. "they can install it, so long as they don't intend to use it" ...
It means manufacturer can install permanent trackers (like RFD tags) for the ostensible purpose of inventory tracking or customer service (like OnStar), but law enforcement can co-opt this for tracking purposes at anytime.