The Fourth Amendment to the United States Constitution protects individuals against unreasonable searches and seizures. Fourth Amendment protections only apply to government action.
In addition, in order for a person to have Fourth Amendment rights, the person must have a reasonable expectation of privacy in the area that is searched. Generally, people have a reasonable expectation of privacy in premises that they own or have a right to possess and in their homes. There is generally no expectation of privacy in things held out to the public.
Generally, for a search to be considered reasonable, the police must have a valid warrant. A valid warrant is one that is issued by a neutral and detached magistrate; based on probable cause; and particularly describes the place to be search or items to be seized. One of the main purposes of the warrant requirements is "to protect privacy interests by assuring citizens subject to a search or seizure that such intrusions are not the random or arbitrary acts of government agents." Skinner v. Railway Labor Executives' Ass'n, 489 U.S. 602, 621-22 (1989) (citations omitted).
Exceptions to Warrant Requirement
While a warrant is generally required for the police to perform a valid search, in reality, many lawful searches are done without a warrant pursuant to the recognized exceptions to the requirement. Police do not need a valid warrant to perform a search under the following circumstances:
- Search incident to a lawful arrest - When the police arrest an individual, they can search the person and areas into which the person might reach (called the person's wingspan) to obtain a weapon or destroy evidence.
- Automobile - Because of an automobile's mobility, police do not need a warrant to search a vehicle that they have probable cause to believe contains contraband or evidence of a crime. The police can search the entire vehicle, including the trunk and all containers within the vehicle that might contain the object for which they are looking.
- Plain view - A police officer does not need a warrant if he is legitimately on the premises and sees evidence of a crime or contraband; the evidence or contraband is in plain view; and he has probable cause to believe that the item is evidence of a crime.
- Consent - If a person gives voluntary and intelligent consent to a search, no warrant is needed.
- Investigative stop/stop and frisk - A police officer may stop a person if she has reasonable suspicion of criminal activity, and she may do a protective frisk or pat down of the person's outer clothing if she has a reasonable belief that the person may be armed and potentially dangerous.
- Exigency - Warrantless searches or entries can be done where there is a need to prevent imminent danger to others, to give emergency help or to prevent the destruction or hiding of evidence. Examples of exigency include an officer in hot pursuit of a fleeing felon and evanescent evidence such as a blood sample containing alcohol.
- Entry to arrest with arrest warrant - A police officer does not need a search warrant if he has an arrest warrant and enter the arrestee's home to make the arrest. For "Fourth Amendment purposes, an arrest warrant founded on probable cause implicitly carries with it the limited authority to enter [without a search warrant] a dwelling in which the suspect lives when there is a reason to believe the suspect is within." Payton v. New York, 445 U.S. 573 at 602-603 (1980).
- Administrative searches - Searches done for administrative or regulatory purposes (for example, health, fire or building inspections) rather than investigatory purposes generally require a warrant. Standards for administrative warrants are different than criminal search warrants. Despite the general warrant requirement, "a warrant may not be constitutionally required when Congress has reasonably determined that warrantless searches are necessary to further a regulatory scheme and the federal regulatory presence is sufficiently comprehensive and defined that the owner of commercial property cannot help but be aware that his property will be subject to periodic inspections undertaken for specific purposes.'' Donovan v. Dewey, 452 U.S. 594, 600 (1981).
- Inventory searches - A police officer does not need a warrant to search a car if she has lawfully seized the car for a parking violation and needs to inventory the car's contents. This exception also applies to taking an inventory of a person's personal effects upon arrest. This exception does not apply if police are searching for evidence of a crime, rather than just doing an inventory.
- Search of probationer's home - A probation officer does not need a warrant or probable cause to search a probationer's home so long as there is a valid state law that allows such searches based on reasonable suspicion.
- Searches of offices of public employees - A public employer does not need a warrant to search an employee's office to look into work-related misconduct or for other work-related reasons that are non-investigatory in nature.
- Drug tests - Because of the government's special needs, there is no warrant requirement for restricted, suspicionless drug and alcohol tests on certain Customs Service employees. In addition, in 2002, the Supreme Court held that random drug testing of all students who participate in "competitive extracurricular activities" is permissible.
The exclusionary rule holds that any evidence obtained in an illegal search or seizure is inadmissible in court. This means that it can't be introduced as evidence at trial. The rule applies to the federal courts and state courts. Under the "fruit of the poisonous tree" doctrine, any derivative evidence uncovered because of an illegal search or seizure is also inadmissible. For example, if the police illegally entered a person's home and discovered a receipt from a storage locker and then went to the storage locker and found drugs, the drugs would be inadmissible as fruit of the poisonous tree. There are exceptions to the exclusionary rule, which are not addressed here.
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