Not every search, seizure, or arrest must be made pursuant to a lawfully executed warrant. The Supreme Court has ruled that warrantless police conduct may comply with the Fourth Amendment so long as it is reasonable under the circumstances. The exceptions made to the Fourth Amendment's warrant requirement reflect the Court's reluctance to unduly impede the job of law enforcement officials. The Court has attempted to strike a balance between the practical realities of daily police work and the privacy and freedom interests of the public. Always requiring police officers to take the time to complete a warrant application and locate and appear before a judge could result in the destruction of evidence, the disappearance of suspects and witnesses, or both. The circumstances under which a warrantless search, seizure, or arrest is deemed reasonable generally fall within seven categories.

1) No warrant is required for a felony arrest in a public place, even if the arresting officer had ample time to procure a warrant, so long as the officer possessed probable cause that the suspect committed the crime. Felony arrests in places not open to the public generally do require a warrant, unless the officer is in "hot pursuit" of a fleeing felon (see Warden v. Hayden, 387 U.S. 294 [1967]). The Fourth Amendment also allows warrantless arrests for misdemeanors committed in an officer's presence.

2) No warrant is required for searches incident to lawful arrest. If a police officer has made a lawful arrest, with or without a warrant, the Fourth Amendment permits the officer to conduct a search of the suspect's person, clothing, and all of the areas within the suspect's immediate reach. This kind of warrantless search is justified on grounds that it allows police officers to protect themselves from hidden weapons that might suddenly be wielded against them. Accordingly, officers are only permitted to seize items from the area in the immediate control of the arrestee.

3) Automobiles may be stopped if an officer possesses a reasonable and articulable suspicion that the motorist has violated a traffic law. Once the vehicle has pulled to the side of the road, the Fourth Amendment permits the officer to search the vehicle's interior, including the glove compartment. However, the trunk of a vehicle cannot be searched unless the officer has probable cause to believe that it contains contraband or the instrumentalities of criminal activity. But similar to a search incident to arrest, once a vehicle has been lawfully impounded, its contents may be inventoried without a warrant, including the contents of the trunk.