Summary
The fourth amendment can be broken down into 2 distinct parts. The first part provides protection against unreasonable searches and seizures, although historically there have been myriad ways in which unreasonable searches were remedied. Modern jurisprudence has afforded the police officers an incentive to respect the amendment.
The second part of the amendment provides for the proper issue of warrants. When warrants are issued, there must be probable cause. Probable cause is tested using the "totality of circumstances" test as defined in Illinois v. Gates, 462 U.S. 213 (1983).
Another way to bifurcate the amendment is to see that one part deals with physical arrests and force by the state (police) and the other part deals with searching and seizing the person's effects: home and personal property.
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Reasonable expectation of privacy
Not every incident where an officer ascertains information is considered a "search." An officer who views something which is publicly viewable (for instance, by looking through the window of a house from the street) is not conducting a "search" of the house. In Katz v. United States, 389 U.S. 347 (1967), the Supreme Court ruled that there is no search unless an individual has an "expectation of privacy" and the expectation is "reasonable"—that is, it is one that society is prepared to recognize. So, for example, there is generally no search when officers look through garbage because there is no expectation that garbage is private (see California v. Greenwood, 486 U.S. 35 (1988)). Similarly, there is no search where officers monitor what phone numbers an individual dials (Smith v. Maryland, 442 U.S. 735 (1979), although Congress has placed statutory restrictions on such monitoring). This doctrine sometimes leads to somewhat unexpected results; in Florida v. Riley, 488 U.S. 445 (1989), the Supreme Court ruled that there was no expectation of privacy (and thus no search) where officers hovered in a helicopter 400 feet above a suspect's house and conducted surveillance.
The Supreme Court has also ruled that there can be no expectation of privacy in illegal activity. Therefore, investigations that reveal only illegal activity (such as some use of drug sniffing dogs) are not searches.
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Searches and seizures without warrants
A warrant is not necessary for a search or seizure under certain circumstances. Officers may search and seize objects that are in "plain view." Before the search and seizure, however, the officers must have probable cause to believe that the objects are contraband.
Similarly, "open fields"—pastures, open water, woods and other such areas—may be searched without warrant, on the basis that the individuals conducting activities therein had no reasonable expectations of privacy. Contrary to its apparent meaning, the "open fields" doctrine has been expanded to include almost any open space other than the land immediately surrounding a domicile (for instance, in Oliver v. United States 466 U.S. 170 (1984), the police ignored a "no trespassing" sign, trespassed onto the suspect's land without a warrant, followed a path several hundred yards, and discovered a field of marijuana. The Supreme Court ruled that no search had taken place. See also: open fields doctrine.
There are also "exigent circumstances" exceptions to the warrant requirement-for instance, if an officer reasonably believes that a suspect may destroy evidence, he might be permitted to seize the evidence without a warrant.
The Supreme Court has also held that individuals in automobiles have a reduced expectation of privacy, because vehicles generally do not serve as residences or repositories of personal effects. Vehicles may not be randomly stopped and searched; there must be probable cause or reasonable suspicion of criminal activity. Items in "plain view" may be seized; areas that could potentially hide weapons may also be searched. With probable cause, police officers may search any area in the vehicle. They may not, however, extend the search to the vehicle's passengers without probable cause to search those passengers.
Under common law, a police officer could arrest an individual (arrests constitute seizures, at least for the purpose of the Fourth Amendment) if that individual committed a misdemeanor in the officer's presence, or if the officer had probable cause to believe that the individual committed a felony. The Supreme Court has applied the common law rule in American jurisprudence. The officer in question must have had probable cause before making the arrest; evidence discovered after the arrest may not be retroactively used to justify the arrest.
The person must also be under arrest to allow a search to be relevant. A person merely detained, such as someone pulled over for a traffic stop, is not "under arrest"; once the traffic ticket is written there is no right to search without permission as no further search could possibly provide any additional evidence regarding the stop. A search without permission after a speeding ticket was written that discovered marijuana was determined to be unlawful under these conditions. Knowles v. Iowa, 525 US 113 (1998)
Another common law rule—that permitting searches incident to an arrest without warrant—has been applied in American law. The justification for such a search is that the arrested individual must be prevented from destroying evidence or using a weapon against the arresting officer. In Trupiano v. United States, 334 U.S. 699 (1948), the Supreme Court held that "a search or seizure without a warrant as an incident to a lawful arrest has always been considered to be a strictly limited right. It grows out of the inherent necessities of the situation at the time of the arrest. But there must be something more in the way of necessity than merely a lawful arrest." In United States v. Rabinowitz, 339 U.S. 56 (1950), the Court reversed its previous ruling, holding that the officers' opportunity to obtain a warrant was not germane to the reasonableness of a search incident to an arrest. The decision suggested that any area within the "immediate control" of the arrestee could be searched, but it did not define the term. In deciding Chimel v. California, 395 U.S. 752 (1969), the Supreme Court elucidated its previous decisions. It held that when an arrest is made, it is reasonable for the officer to search the arrestee for weapons and evidence. Similarly, it was held that it is reasonable for the officer to search the area within the arrestee's immediate control, that is, the area from which the defendant may gain access to a weapon or evidence. A search of the room in which the arrest is made is therefore permissible, but the same is not true of a search of other rooms, as the arrestee would not probably be able to access weapons or evidence in those rooms at the time of arrest.
The reasonable grounds standard is further applied to searches of homes of individuals on probation.
It has been held that searches in public schools require neither warrants nor probable cause. (See New Jersey v. T. L. O., 468 U.S. 325 (1985)). It is merely necessary that the searching officers have reasonable grounds for believing that the search will result in the finding of evidence of illegal activity. Government offices may be searched for evidence of work-related misconduct by government employees on similar grounds. Searches of prison cells are subject to no restraints relating to reasonableness or probable cause; neither are searches conducted at the border (the "border search exception) (see United States v. Ramsey, 431 U.S. 606 (1977); United States v. Montoya de Hernandez, 473 U.S. 531 (1985); United States v. Flores-Montano, 541 U.S. __ (2004)) or searches undertaken as a condition of parole (see Samson v. California, 546 U.S. __ (2006). Finally, a search is reasonable if the target without coercion consents to the search, even if the target is unaware and not told about their right to refuse to cooperate.
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Conditions of searches
In general, a few things have been established. First, in an instance where a person has not been arrested and a search must be conducted in an area where a person has a reasonable expectation of privacy, law enforcement officials are required to gain permission from an arbiter, i.e. the courts, in order to be allowed to search someone. It is, for example, unlawful to force someone to undergo surgery to uncover incriminating evidence because that would interfere with the privacy of the human body. The application of this has been vague, however. Under HIPAA, for example, federal agents are allowed to search medical records through administrative subpoenas, which do not require court approval.
Also, the courts have established that in certain cases, probable cause is not necessary in order to conduct a search. If a police officer suspects you may present a threat to others, he has the right to frisk you on reasonable suspicion (see Terry v. Ohio, 392 U.S. 1 (1968)). If you are driving drunk, you are likewise open to be searched on reasonable suspicion. In the case of random drug tests, no probable cause must be established in order to force you to be tested.
Regarding what level of notification must be provided to those who are to be searched: in some cases, notification of not only being searched, but also what is being searched, is necessary. For example, if you are being provided the service of a pregnancy test, and your sample is used to determine whether or not you have used illicit drugs, that is an illegal means of search if you are not informed. In certain cases the courts have found that where there is reason to believe that notification will lead to the destruction of evidence or the endangerment of lives, the government is not required to notify the searched party. This has been applied in the case of delayed notification, where the government is not required to inform you that you or your residence has been searched. It remains difficult to determine, though, whether certain federal actions are truly legal, or are merely the result of poorly defined legal boundaries.
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Exclusionary rule
See also: exclusionary rule
At common law, all evidence, no matter how seized, could be admitted in court. In Weeks v. United States, 232 U.S. 383 (1914), however, the Supreme Court adopted the "exclusionary rule," under which evidence seized unlawfully is rendered inadmissible in court. The rule was made applicable to the states in Mapp v. Ohio 367 U.S. 643 (1961).
The exclusionary rule serves primarily to deter police officers from conducting unlawful searches and seizures. It has, however, a number of exceptions. In United States v. Leon, 468 U.S. 897 (1984), the Supreme Court applied the "good faith" rule and held that evidence seized by officers objectively and in good faith relying on a warrant later found to be defective was still admissible. The evidence would still be excluded if an officer dishonestly or recklessly prepares an affidavit forming the basis of the warrant, if the issuing magistrate abandons his neutrality, or if the warrant lacks sufficient particularity. It remains unclear whether the "good faith" exception applies to warrantless seizures. On January 8, 1974, the Supreme Court ruled that grand juries may use illegally obtained evidence in questioning witnesses. United States v. Calandra, 414 U.S. 338.
The Supreme Court has held the rule does not apply in certain situations: (1) probation or parole revocation hearings; (2) tax hearings; (3) deportation hearings; (4) when government officials illegally seize evidence outside the United States; (5) when a "private actor" (i.e., not a State employee) illegally seized the evidence; or (6) when the illegally seized evidence is used to impeach the defendant's testimony. Furthermore, a defendant has standing to object to the admission of unconstitutionally seized evidence only if such seizure violated his own Fourth Amendment rights; a defendant may not assert the rights of a third party.
Closely related to the exclusionary rule is the "fruit of the poisonous tree" doctrine, under which the government is prohibited from introducing any evidence that was obtained subsequent to and as a result of the illegal search.
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