The Fourth Amendment protects persons against unreasonable searches and seizures by law enforcement officers. Generally, a search warrant is required before an officer may search a person or place. This general requirement is waived for many searches and seizures, including a search incident to a lawful arrest, a stop and frisk for weapons, a seizure of items in plain view, a search of an automobile, a search consented to by the suspect, a search after a hot pursuit, and a search in exigent, or emergency, circumstances. When an officer seeks a search warrant, the officer must present evidence to a judge or magistrate. The evidence must be sufficient to establish probable cause that evidence of a crime will be found at the place to be searched.
Probable cause is a level of belief beyond mere suspicion but short of full certainty.
Whether an officer can establish probable cause to obtain a search warrant depends on the facts of the case. For example, if an arrested person is discovered with a small amount of marijuana, this alone will not justify a search of the person's home. However, if the person is discovered with a large amount of marijuana, the quantity may support the suspicion that more marijuana may be found in the person's home, and the large amount may be used as the basis for obtaining a search warrant. Police officers seeking a search warrant must state, under oath and with particularity, the facts supporting probable cause. If the search warrant is later found to be lacking in probable cause, or if important statements made by the officers are found to have been intentionally misleading, the evidence seized pursuant to the warrant may be excluded from trial.