Law enforcement GPS tracking: how widespread?

After the recent Supreme Court decision ruling unconstitutional at least certain types of warrantless tracking of automobiles with GPS devices attached to the cars, the FBI has apparently turned off many of its trackers.

After the ruling, the FBI had a problem collecting the devices that it had turned off, Mr. Weissmann said. In some cases, he said, the FBI sought court orders to obtain permission to turn the devices on briefly – only in order to locate and retrieve them.

What I find interesting is that it appears that around 3,000 of the devices were deactivated.  That represents 3,000 people who up to a couple of weeks ago were secretly tracked by their government without the minimum requirement of a simple search warrant. Not a huge number, but it is the number of devices in operation at one point in time. The number of people tracked by the FBI over the past several years is probably at least 180,000, assuming 30 days per person tracked over five years. And this estimate only covers the FBI. Surely other Federal agencies were using the same techniques.

This represents a significant victory over the continuing erosion of privacy rights in the United States.