The Fourth Amendment to the United States Constitution guarantees the protection of the people of United States, their personal documents, and their residences from unreasonable searches and seizures. In order to conduct a lawful search, law enforcement officials must first present facts before a judge that justify suspicion of wrongdoing by a person, and then obtain a search warrant permitting the search. Exemptions from the Fourth Amendment protections, however, are allowed when pressing circumstances make the search imperative. Law enforcement officials may search without a warrant when the owner of a residence consents to their entry. In addition, officers or officials may conduct warrantless searches in certain notable locations or settings.
A condition of parole, probation, or supervised release is that law enforcement personnel have the legal right to examine the vehicle, workplace, home, and body of the released person without probable cause or even reasonable suspicion. Probable cause, which is normally required for a search, refers to a collection of facts generated through systematic analysis that would cause a reasonable person to conclude that someone is guilty of a crime. Under court supervision, officers can enter into the parolee's property without giving a warning or reason and search the commonly used rooms of the house, such as the kitchen, family room, and bathroom. The personal bedroom of the parolee may also be searched. The possessions and fixtures of other occupants of the house are also subject to search if they are located in common areas.
Following an arrest, officers can search the body and personal effects of the suspect. For an indoor arrest, the officers can search the zone around the suspect for a distance that the suspect could jump or throw something. Officers can also collect samples of fingernail scrapings or blood, in order to retain potential evidence that may otherwise vanish. After arrests of an individual in an automobile, the officers may search the passenger compartment. If they have probable cause to believe that proof of a crime can be found in the vehicle, they can check the vehicle, including any containers in the car, without a warrant.
The courts have determined that testing for drugs is constitutional under certain circumstances as forms of warrantless searches. Employees in certain high-risk or high-security jobs can be required to drug test. Bus drivers, railroad workers, airline pilots, and U.S. Customs agents may all be subjected to drug testing. Public school students can be mandated to comply with random drug testing in order to engage in chorus, sports, band, or academic competitions. Professional athletes and participants in international competitions, such as the Olympics, are also required to submit bodily fluid samples for analysis as a condition for participation.
Emergency responses also permit an exemption from the Fourth Amendment protection against warrantless searches. Cries for help, screams, or other indications of distress give officers the right to enter a residence immediately for the purpose of protection as well as apprehension. Law enforcement officials can enter a home when there is immediate danger from a fire or other hazard, either to manage the problem, to rescue involved persons, or to gather evidence regarding the origin of a fire or other disturbance for a limited time. Judges usually find that in cases where the officers had less than 30 minutes to respond, proceeding without a warrant is valid. High-speed chases and "hot pursuits" are urgent situations that also allow warrantless searches.
Certain warrantless searches are permitted by virtue of the environment in which the search is being conducted. For example, school officials can search a student on school grounds as well as the student's backpack, purse, and other personal items if they have “reasonable suspicion” that the student has broken the law or a school rule. The United States Supreme Court has not yet ruled on whether a pupil has a right to privacy regarding his desk or locker. Various lower courts have produced conflicting opinions. In addition, airline passengers may be obligated to pass through metal detectors and comply with searches of their bodies and their possessions before getting on an airplane.