Always read the primary source is my motto:
I think I finally understand why Schmidt, et. al., have gone on record (while clearly smart enough to know the ire that it would raise in the geek community) that '[we] do not have a reasonable expectation of privacy' when using their systems.
The first case, Knotts, upheld against Fourth Amendment
challenge the use of a “beeper” that had been placed in
a container of chloroform, allowing law enforcement to
monitor the location of the container. 460 U. S., at 278.
We said that there had been no infringement of Knotts’
reasonable expectation of pri- vacy since the information
obtained—the location of the automobile carrying the
container on public roads, and the location of the off-loaded
container in open fields near Knotts’ cabin—had been
voluntarily conveyed to the pub- lic.6 Id., at 281–282.
But as we have discussed, the Katz reasonable-expectation-
of-privacy test has been added to, not substituted for,
the common-law trespassory test. The holding in Knotts
addressed only the former, since the latter was not at
issue. The beeper had been placed in the container before
it came into Knotts’ possession, with the consent of the
then-owner. 460 U. S., at 278. Knotts did not challenge
that installation, and we specifically de- clined to consider
its effect on the Fourth Amendment analysis. Id., at 279, n.
Knotts would be relevant, per- haps, if the Government were
making the argument that what would otherwise be an
unconstitutional search is not such where it produces only
public information. The Government does not make that
argument, and we know of no case that would support it.