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.