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 will provide any additional evidence regarding the stop could possibly be uncovered. 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. 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.

In most jurisdictions, an arrest warrant is required for misdemeanors that do not occur within view of a police officer. However, as long as police have the necessary probable cause, a warrant is usually not needed to arrest someone suspected of a felony.

The Fourth Amendment to the United States Constitution protects people from unreasonable government intrusions into their legitimate expectations of privacy.  A warrantless search is presumed to be illegal.  (Mincey v. Arizona (1978) 437 U.S. 385, 390.)  The prosecution always has the burden of justifying the search by proving the search fell within a recognized exception to the warrant requirement.  (In re Tyrell J. (1994) 8 Cal.4th 68, 76.)(see CalCaseLaw.Com-People v. Williams B188129-12/13/06 CA2/8)