> It's a simple extension of a very old principle: you don't have an expectation [of privacy] on areas viewable from public property.
Wandering off-topic just a bit, there's an oddball trade-secret case from 1970 that has always puzzled me: A father-and son photographer team flew over a DuPont chemical plant that was under construction and took aerial photographs. DuPont tracked down the photographers and asked who had hired them; when they refused to say, DuPont sued them for theft of trade secrets.
The photographers moved to dismiss, in part on grounds that aerial photography from the public airspace was fair game. The appeals court upheld the trial court's ruling rejecting the photographers' contention and said they could be compelled to disclose who hired them.
The appellate court said, "To require DuPont to put a roof over the unfinished plant to guard its secret would impose an enormous expense to prevent nothing more than a school boy's trick. We introduce here no new or radical ethic since our ethos has never given moral sanction to piracy. The market place must not deviate far from our mores. We should not require a person or corporation to take unreasonable precautions to prevent another from doing that which he ought not do in the first place. Reasonable precautions against predatory eyes we may require, but an impenetrable fortress is an unreasonable requirement, and we are not disposed to burden industrial inventors with such a duty in order to protect the fruits of their efforts." [1].
Tailing someone on a public road is a very old principle as well, but that didn't matter Alito and the other three justices who joined with him in the Jones concurrence. He found that 24/7 monitoring for 28 days on public roads only with a GPS device constituted a search. I don't think the FBI did anything wrong here, but you're drastically oversimplifying what surely is an un-litigated issue. The fact that a GPS device was so much cheaper than 24 hour surveillance via a tail car is what Alito's concurrence hinged on, despite the fact that the monitoring was exactly the same.