Why is there no reasonable expectation of privacy in open fields? Why does the open fields doctrine ...

For a property to fall within the category of open fields where there is no
reasonable expectation of privacy, these areas must not provide settings for the
intimate activities that the Fourth Amendment was designed to protect from
government interference or surveillance. The Fourth Amendment protects people in
their persons, houses, papers, and effects.. Thus, even looking at the Amendment in
a pure textual sense, it is easy to see that it was not meant to protect open, privatelyowned land.
Posting a No Trespassing sign does not mean that the open field doctrine may not
apply and exclude the posted property from protection of the Fourth Amendment. The
Supreme Court has decided that if this was all that was needed to give owners a
reasonable expectation of privacy in an area where they could not otherwise expect
such, police officers would have to guess before every search as to whether owners
have posted a sufficient number of warnings or posted them in adequate places to
protect the property. This would make the job of the police very difficult, as they must
be able to know with a reasonable degree of certainty what is protected by the Fourth
Amendment and what is not.

Confirmed correct