Unfortunately for privacy itself, the Fourth Amendment does permit searches and seizures that are considered to be reasonable. In practice, this means that the police may override（不顾, 不考虑（某人的意见,决定,愿望等））your privacy concerns and conduct a search of your home, barn, car, boat, office, personal or business documents, bank account records, trash barrel or wherever, if:
· the police have probable cause to believe they can find evidence that you committed a crime, and a judge issues a search warrant （see Section II）, or
· the search is proper without a warrant because of the particular circumstances.
2. Are All "Searches" Subject to Fourth Amendment Protection?
No. American judges have written thousands of opinions interpreting the Fourth Amendment and explaining what a "reasonable" search is. But before getting to that question, another question must be answered first. Did the search in question violate the defen-dant's privacy in the first place? Or more precisely, as framed（构成, 设计, 制定） by the U.S. Supreme Court, did the defendant have a "legitimate expectation of privacy" in the place or thing searched? （Katz v. U.S., 1967.） If not, then no "search" occurred for the purpose of Fourth Amendment protection. If, however, a defendant did have a reasonable expectation of privacy, then a search did occur, and the search must have been a reasonable one.
Courts use a two-part test （fashioned by the U.S. Supreme Court） to determine whether, at the time of the search, the defendant had a legitimate expectation of privacy in the place or things searched.
· Did the person subjectively （actually） expect some degree of privacy?
· Is the person's expectation objectively reasonable, that is, one that society is willing to recognize?
Only if the answer to both questions is "yes" will a court go on to ask the next, ultimate question: Was the search reasonable or unreasonable?
For example, a person who uses a public restroom expects not to be spied upon （the person has a subjective expectation of privacy） and most people—including judges and juries—would consider that expectation to be reasonable （there is an objective expectation of privacy as well）. Therefore, the installation of a hidden video camera by the police in a public restroom will be considered a "search" and would be subject to the Fourth Amendment's requirement of reasonableness.
On the other hand, when the police find a weapon on the front seat of a car, it is not a "search" for Fourth Amendment purposes because it is very unlikely that the person would think that the front seat of the car is a private place （a subjective expectation of privacy is unlikely）, and even if the person did, society is not willing to extend the protections of privacy to that particular location （no objective expectation of privacy）.