The Fourth Amendment to the United States Constitution provides that: The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized. Translation: No unreasonable search and seizures and no warrant unless there is probable cause, an oath, and a particular description.
A foundational element for this right is that the individual has a reasonable and justifiable expectation of privacy because if not, then the government can intrude. Government intrusion into an are that is reasonably and justifiably private is a search, whereas, a seizure is the exercise of control over a person or a thing.
Michigan v Chestnut, 486 US 567 (1988) helps define what is a seizure. When a reasonable individual would assume that they are not free to leave, they are seized, and a police pursuit of a suspect is not such a seizure. There must be a physical application of force or a submission to a show of force. California v Hodari D., 499 US 621 (1991). One must consider the totality of circumstances in determining whether a reasonable person would feel that they are free to leave or to refuse an officer’s request. Florida v Bostick, 501 US 429 (1991).
Arrests are seizures and must be based upon probable cause and generally do not require a warrant if they take place in public. United States v Watson, 423 US 411 (1976). Beck v Ohio, 379 US 89 (1964) provides that probable cause to arrest includes having reasonable trustworthy facts and circumstances to warrant a reasonably prudent person to believe that the suspect has committed a crime or is committing a crime. For felony crimes all it takes are reasonable grounds to believe that a felony has been committed by the person to be arrested without a warrant. For misdemeanor crimes, if they are committed in the “presence” of the police officer, then the officer may make a warrantless arrest. “Presence” includes knowledge through any of the senses.
Arrests in the home without an emergency require a warrant. Payton v New York, 445 US 573 (1980). The presumption is that a warrantless search of a home is unreasonable and therefore, it is the government’s burden to overcome this presumption by showing exigent circumstances. Welsh v Wisconsin, 466 US 740 (1984).
A person can be detained but not arrested, such as with an investigatory detention, an automobile stop, or while on premises being searched. To conduct an investigatory detention a.k.a. stop and frisk, the police must have a reasonable suspicion supported by articulable facts of criminal activity / involvement. Terry v Ohio, 392 US 1 (1968). To conduct an automobile stop, the police must have a reasonable belief that a traffic law has been violated. Delaware v Prouse, 440 US 648 (1979). Finally, to detain an individual, the police must possess a valid warrant to search for contraband. Michigan v Summers, 452 US 692 (1981).