21.1 Fourth Amendment: Searches, Seizures, Arrests & Warrants

21.1 Fourth Amendment: Searches, Seizures, Arrests & Warrants

NCBE's outline tests the Fourth Amendment under three headings: arrests and other detentions, evidentiary search and seizure (including warrants and their exceptions), and the exclusionary rule. This section covers whether a search or seizure occurred and what a valid arrest or warrant requires. Warrant exceptions are covered in Section 21.2, and the exclusionary rule and standing in Section 21.3.

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The Fourth Amendment Threshold: Government Action

The Fourth Amendment exclusively constrains state action. Purely private searches or seizures—no matter how wrongful, illegal, or intrusive—do not implicate the Fourth Amendment (Burdeau v. McDowell).

• Private Citizens: If a suspicious neighbor, private landlord, or corporate investigator burglarizes a suspect's home, discovers narcotics, and turns them over to the police, the evidence is admissible in a criminal prosecution because no government search occurred.
• Government Agents: A search conducted by a private individual becomes state action if law enforcement instigates, directs, participates in, or explicitly encourages the search. The test is whether the private actor, in light of all the circumstances, acted as an "instrument or agent" of the state.
• Public Officials: All public law enforcement officers, federal agents, public school administrators, and private security guards deputized with special police powers constitute government actors.

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Defining a "Search": Two Independent Constitutional Tests

Historically, the Fourth Amendment was tied strictly to common-law property trespass. Today, the Supreme Court recognizes two co-existing, independent tests to determine whether police conduct constitutes a search:

                      ┌──────────────────────────────────────────────┐
                      │       Did Government Action Occur?           │
                      └──────────────────────┬───────────────────────┘
                                             │ YES
                                             ▼
                      ┌──────────────────────────────────────────────┐
                      │  Did the Government physically intrude on    │
                      │  a person, house, paper, or effect to        │
                      │  gather information? (Trespass - Jones)      │
                      └──────────────┬───────────────────────────────┘
                                     │
                         YES         │          NO
                         ▼           │          ▼
               ┌───────────────────┐ │ ┌──────────────────────────────────┐
               │ CONSTITUTIONAL    │ │ │ Did government invade an actual, │
               │ SEARCH OCCURRED   │ │ │ subjective expectation of privacy│
               │ (Warrant/Exception│ │ │ that society recognizes as       │
               │  Required)        │ │ │ reasonable? (Katz REP Test)      │
               └───────────────────┘ │ └────────────────┬─────────────────┘
                                     │                  │
                                     │        YES       │        NO
                                     │        ▼         │        ▼
                                     │  ┌─────────────┐ │  ┌──────────────┐
                                     │  │ SEARCH      │ │  │  NO SEARCH   │
                                     │  │ OCCURRED    │ │  │  4th Amend.  │
                                     │  └─────────────┘ │  │  Inapplicable│
                                     │                  │  └──────────────┘

1. The Katz Reasonable Expectation of Privacy (REP) Test

In Katz v. United States (1967), the Supreme Court ruled that the Fourth Amendment "protects people, not places." In his landmark concurrence, Justice Harlan established the two-pronged test that defines a modern search:

1. Subjective Expectation: The individual must exhibit an actual, subjective expectation of privacy in the place or item searched (i.e., took affirmative steps to shield it from public view).
2. Objective Reasonableness: That subjective expectation must be one that society is prepared to recognize as objectively legitimate and reasonable.

2. The Property Trespass Test (Jones and Jardines)

The Katz privacy test did not displace common-law trespass; it supplemented it. If government agents physically trespass onto a constitutionally protected area—persons, houses, papers, or effects—with the intent to obtain information, a search has occurred as a matter of law, regardless of whether the suspect held an expectation of privacy.

• United States v. Jones (2012): Law enforcement officers attached a GPS tracking device to the undercarriage of a suspect's Jeep while it was parked on a public lot and monitored its movements for 28 days. The Court held that an automobile is an "effect," and the physical attachment of the device to collect intelligence was a common-law trespass amounting to a Fourth Amendment search.
• Florida v. Jardines (2013): Officers brought a trained drug-detection dog onto the front porch of a home to sniff around the base of the front door. The porch is part of the home's curtilage. While ordinary visitors possess an implied customary license to approach a front door, knock, and wait briefly, deploying a specialized sensory device to conduct a forensic investigation exceeds that license. The physical trespass on the curtilage constituted a search.

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Protected vs. Unprotected Areas

The boundary between protected and unprotected spaces is heavily tested on the MBE. An individual lacks a reasonable expectation of privacy in anything they voluntarily expose to the public view or third parties.

Highly Protected Areas

• The Home: The home sits at the apex of Fourth Amendment protection. Physical entry into a private home without a warrant is presumptively unreasonable (Payton v. New York).
• The Curtilage: The curtilage is the land immediately surrounding and intimately associated with the home and the privacies of domestic life. Under United States v. Dunn (1987), courts weigh four factors to identify curtilage: (1) proximity to the home; (2) whether the area is within an enclosure surrounding the home; (3) nature of uses to which the area is put; and (4) steps taken to protect the area from observation by passersby.
• Hotel Rooms & Overnight Guests: Overnight guests have a legitimate expectation of privacy in their host's home (Minnesota v. Olson). Commercial guests present solely for brief business transactions (e.g., bagging cocaine for two hours) do not (Minnesota v. Carter).
• Sealed Luggage and Personal Effects: Opaque, closed containers and personal baggage carry a full expectation of privacy against physical tactile manipulation (Bond v. United States).

Unprotected Areas (No Reasonable Expectation of Privacy)

Modern Exception — Historical Cell-Site Location Information (CSLI): In Carpenter v. United States (2018), the Supreme Court created an exception to the Third-Party Doctrine: obtaining historical CSLI spanning seven or more days from a wireless carrier constitutes a Fourth Amendment search requiring a warrant based on probable cause, given the uniquely comprehensive and invasive record of a person's physical movements.

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Seizures of Persons

A seizure of a person occurs when, under the totality of the circumstances, a reasonable person would believe they are not free to leave or terminate the encounter (United States v. Mendenhall). Under California v. Hodari D. (1991), a seizure requires either:

1. The application of physical force to the body with intent to restrain (even if slight and even if the suspect escapes, Torres v. Madrid, 2021); or
2. Submission to an assertion of authority (if an officer shouts "Stop in the name of the law!" and the suspect flees, no seizure occurs until the suspect is physically tackled or stops and complies).

Tiers of Personal Encounters

• Consensual Encounter: Officers approach an individual in public, ask questions, or request identification without displaying weapons or making demands. No justification or suspicion required. The citizen is free to decline and walk away.
• Investigatory Detention (Terry Stop): Brief, temporary investigatory stop. Requires Reasonable Articulable Suspicion (RAS) based on specific, objective facts that criminal activity is afoot (Terry v. Ohio). An inchoate hunch is legally insufficient.
• Custodial Arrest: Full physical deprivation of liberty. Requires Probable Cause (PC)—objective facts and circumstances sufficient to warrant a prudent officer in believing the suspect has committed or is committing a crime.

Traffic Stops

A traffic stop constitutes a Fourth Amendment seizure of the driver and all passengers (Brendlin v. California). Passengers have standing to challenge the constitutional validity of the initial stop.

• Pretextual Stops Valid (Whren v. United States): If an officer observes an actual objective traffic violation (e.g., broken taillight, failure to signal), the stop is lawful under the Fourth Amendment, even if the officer's true subjective motivation was to investigate an unrelated hunch regarding narcotics.
• Officer Safety Powers: Officers may routinely order both the driver and all passengers to exit the vehicle during a lawful traffic stop without independent suspicion (Pennsylvania v. Mimms; Maryland v. Wilson).
• Duration Restrictions (Rodriguez v. United States): A traffic stop may last no longer than is reasonably necessary to address the mission of the stop—inspecting driver's license, vehicle registration, proof of insurance, running computer warrant checks, and issuing a citation. Officers cannot prolong a completed traffic stop, even for seven or eight minutes, to conduct a canine sniff without independent reasonable suspicion.

Arrest Warrants and Entry into Dwellings

• Arrests in Public: Police do not need an arrest warrant to arrest a person in a public place, provided they possess probable cause that the person committed a felony (or a misdemeanor committed in the officer's presence) (United States v. Watson).
• Arrests in Suspect's Own Home (Payton v. New York): Absent consent or exigent circumstances, police MUST possess an arrest warrant (and reason to believe the suspect is inside) to enter the suspect's private residence to effectuate an arrest.
• Arrests in a Third Party's Home (Steagald v. United States): Absent consent or exigent circumstances, police armed only with an arrest warrant for a suspect cannot enter a third party's home to search for that suspect. Police must obtain a search warrant for the third party's residence to protect the third party's Fourth Amendment privacy rights.

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Search Warrant Requirements

To be constitutionally valid, a search warrant must satisfy three core requirements:

1. Probable Cause: The supporting affidavit must establish a fair probability that contraband or evidence of a crime will be found in the particular place to be searched. Under Illinois v. Gates (1983), probable cause is evaluated under the totality of the circumstances, replacing the rigid Aguilar-Spinelli two-pronged test. Informant reliability, veracity, and basis of knowledge remain relevant factors, and police corroboration of innocent details can compensate for an informant's deficient track record.
2. Neutral and Detached Magistrate: The issuing official must be an independent judicial officer, detached from law enforcement. A state attorney general, active prosecutor, or magistrate paid a fee only when a warrant is issued (Connally v. Georgia) fails this standard.
3. Particularity: The warrant must describe with reasonable precision the place to be searched (specific street address, apartment unit) and the items to be seized (specific contraband or evidence). General warrants authorizing officers to search a home for "any evidence of illegal activity" are unconstitutional.

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Execution of Warrants & The Good Faith Exception

Execution Rules

• Knock and Announce Rule: Officers executing a search warrant must announce their presence and authority and wait a reasonable time before forcibly entering, unless they possess reasonable suspicion that knocking would be dangerous, futile, or inhibit the effective investigation (e.g., risk of evidence destruction) (Wilson v. Arkansas).
• No Exclusionary Remedy for Knock Violations (Hudson v. Michigan): Even if police violate the knock-and-announce rule by entering prematurely, the Exclusionary Rule does not suppress the evidence seized. The Supreme Court held that the interests protected by knocking (preventing violence and property damage) are attenuated from the discovery of evidence pursuant to a valid warrant.
• Detention of Occupants: Officers executing a valid search warrant for contraband have categorical authority to detain occupants of the premises while the search is conducted (Michigan v. Summers).

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More on Searches, Seizures & Warrants

Technology and the Home

• Thermal imaging: Using a device not in general public use to learn details about the interior of a home that could not otherwise be obtained without physical intrusion is a search (Kyllo v. United States, 2001).
• Aerial observation: Naked-eye observation from public airspace is not a search (California v. Ciraolo; Florida v. Riley), and neither is aerial photography of an industrial complex's open areas (Dow Chemical Co. v. United States, 1986).
• Cell-site records: Acquiring at least seven days of a person's historical cell-site location information from a wireless carrier is a search that generally requires a warrant (Carpenter v. United States, 2018).

Stops, Arrests, and Use of Force

• Anonymous tips: An anonymous tip that a person is carrying a gun, without predictive information showing the tipster's reliability, does not justify a stop and frisk (Florida v. J.L., 2000). A 911 call by an eyewitness reporting that a specific vehicle just ran the caller off the road can supply reasonable suspicion (Navarette v. California, 2014).
• Vehicle records: An officer who learns that a vehicle's registered owner has a revoked license may stop the vehicle, absent information suggesting the owner is not driving (Kansas v. Glover, 2020).
• Mistakes of law: An officer's objectively reasonable mistake about the meaning of a traffic law can supply reasonable suspicion for a stop (Heien v. North Carolina, 2014).
• Probable cause for multiple occupants: Finding cocaine behind a back-seat armrest gave probable cause to arrest all three occupants of a car (Maryland v. Pringle, 2003).
• Minor offenses and state law: A custodial arrest for a fine-only seatbelt violation does not violate the Fourth Amendment (Atwater v. City of Lago Vista, 2001), and an arrest supported by probable cause is constitutional even if state law did not authorize arrest for that offense (Virginia v. Moore, 2008).
• Prompt judicial review: A person arrested without a warrant must receive a judicial determination of probable cause promptly (Gerstein v. Pugh, 1975), generally within 48 hours (County of Riverside v. McLaughlin, 1991).
• Excessive force: Claims that officers used excessive force during an arrest or stop are judged under the Fourth Amendment's objective reasonableness standard (Graham v. Connor, 1989), considering the totality of the circumstances, including events leading up to the moment force was used (Barnes v. Felix, 2025).

Warrant Details

• Anticipatory warrants: A warrant that becomes executable only when a triggering event occurs—such as delivery of a package of contraband—is valid if there is probable cause that the event will occur and that evidence will then be found (United States v. Grubbs, 2006).
• Particularity: A warrant that fails to describe the items to be seized is invalid even if the application described them, unless the application is incorporated into the warrant (Groh v. Ramirez, 2004).
• Reasonable mistakes in execution: Officers who search the wrong apartment because they reasonably believed it was covered by the warrant do not violate the Fourth Amendment (Maryland v. Garrison, 1987).
• People on the premises: A warrant to search premises does not authorize searching everyone present (Ybarra v. Illinois, 1979). Officers may detain occupants during the search (Michigan v. Summers), but not people who have already left the immediate vicinity (Bailey v. United States, 2013).