In Oliver v. United States (1984), the United States Supreme Court revived the open fields doctrine first announced by the court in Hester v. United States (1924). The Oliver court held that "an individual may not legitimately demand privacy for activities conducted out of doors in fields, except in the area immediately surrounding the home." (Oliver, supra, 466 U.S. at p. 178 [104 S. Ct. at p. 1741].) A subjective expectation of privacy in an open fields area is not an expectation that society is willing to recognize as reasonable. (Id. at p. 179 [104 S. Ct. at pp. 1741-1742].) Law enforcement may conduct warrantless observations from open fields; the fact that the observing officer trespasses to get to his or her observation point does not transmute the observation into an unconstitutional search. (Id. at p. 183 [104 S. Ct. at p. 1744].) In defining "open fields area," the court noted that the term "may include any unoccupied or undeveloped area outside of the curtilage. An open field need be neither 'open' nor a 'field' as those terms are used in common speech." (Id. at p. 180, fn. 11 [104 S. Ct. at p. 1742].) A thickly wooded area, for example, may be considered an open field for the purposes of the Fourth Amendment analysis. (Ibid.) 'The touchstone of Fourth Amendment analysis is whether a person has a "constitutionally protected reasonable expectation of privacy. " (People v. Freeman (1990) 219 Cal. App. 3d 894, 900 [268 Cal. Rptr. 603].)