If a criminal exposes evidence in ways that can be detected by use of the personal senses, there is no Fourth Amendment "search" involved in discovering the presence of such items. Assuming no previous unlawful search, the seizure of the items is presumptively reasonable if there is probable cause to associate them with criminal activity. (Payton v. New York)

The U.S. Supreme Court has considered investigative use of all of the senses except taste.

Plain View

"It has long been settled that objects falling in the plain view of an officer who has a right to be in a position to have that view are subject to seizure and may be introduced in evidence." (Harris v. U.S.)

The conditions of this doctrine are that an item whose criminal character is immediately recognizable is in plain view, from a lawful vantage point, and there is a lawful right of access to make the seizure.

Plain Feel

When you have a lawful right to touch an area and your sense of touch, combined with your training and experience, indicates the presence of something seizable, it may be removed. In Minnesota v. Dickerson, an officer who had lawfully detained a drug suspect was performing a justified weapons frisk when he felt a lump of rock cocaine. The Supreme Court ruled that this object could have been lawfully removed from the suspect's pocket if it had been immediately apparent to the officer that it was a controlled substance:

"If a police officer lawfully pats down a suspect's outer clothing and feels an object whose contour or mass makes its identity immediately apparent, its warrantless seizure would be justified by the same practical considerations that inhere in the plain-view context."

However, the court found that the identity of the rock cocaine was not immediately apparent to the officer upon first touch, but only became apparent through continued manipulation, which constituted an unlawful search and rendered the drugs inadmissible. To rely on the plain feel exception, officers must make clear that they immediately recognized the nature of the seized object as soon as it was felt, without further manipulation.

Plain Smell

Some distinctive odors can be detected by humans (burnt marijuana, for example); some can be detected by trained dogs (drugs, explosives, etc.). Merely smelling the air surrounding a suspect, his vehicle, or some container does not constitute a search. If the odor reveals the presence of seizable objects, they may be seized.

In U.S. v. Place, the Supreme Court ruled that exposing a traveler's luggage to sniffing by a drug K-9 did not infringe the owner's privacy rights: "The sniff discloses only the presence or absence of narcotics, a contraband item. Therefore, exposure of the luggage to a trained canine did not constitute a 'search' within the meaning of the Fourth Amendment."

The court applied the same principle in Illinois v. Caballes, finding no error where the K-9 was walked around a motorist's car during a traffic stop. The dog alerted to the trunk, where officers found narcotics. The court said, "A dog sniff conducted during a lawful traffic stop that reveals no information other than the location of a substance that no individual has a right to possess does not violate the Fourth Amendment."

Plain Hearing

Officers or undercover agents can position themselves in accessible locations where they can overhear criminal conversation without any extraordinary listening devices (such as wiretaps or parabolic microphones). Anything overheard can be used in evidence.

In Hoffa v. U.S., for example, a government informant who had been invited to Hoffa's hotel room listened to statements about plans to bribe witnesses in the labor leader's ongoing trial. These statements were reported to federal agents and were introduced in evidence. The Supreme Court upheld admissibility, ruling that "The Fourth Amendment does not protect a wrongdoer's misplaced belief that a person to whom he voluntarily confides his wrongdoing will not reveal it."

Plain Shape

A variation of the plain-view doctrine can be found in comments from the court indicating that when the distinctive shape of a container reveals the contents as something seizable, there is no Fourth Amendment "search" involved in opening the container and retrieving the contents:

"Some containers (for example, a kit of burglar tools or a gun case) by their very nature cannot support a reasonable expectation of privacy because their contents can be inferred from their outward appearance." (Arkansas v. Sanders)

"The police must have reasonable grounds to believe that the particular package carried by the citizen is contraband. Its shape and design might at times be adequate. The weight of it and the manner in which it is carried might at times be enough." (U.S. v. Henry)

Based on these principles, lower courts have found that the shape and packaging of various items allowed officers to open containers and seize the weapons, evidence, or contraband they contained. Examples include bricks of marijuana, heroin balloons, foil bindles of drugs, gun cases, and hide-a-key boxes.


Examination of the outside of a car in a parking lot for murder evidence. (Cardwell v. Lewis)

Seizure of robbery weapons while serving a search warrant for the stolen property. (Horton v. California)

Narcotics on a table inside a residence lawfully entered. (Washington v. Chrisman)

Suspect's clothing seen during a lawful search of a residence for other suspects. (Warden v. Hayden; Maryland v. Buie)


Plain View-allows seizure of apparent criminal items seen with lawful access

Plain Feel-where an item is felt during lawful touching and is immediately apparent as contraband or a weapon, it can be retrieved

Plain Smell-both officers and trained dogs can use the olfactory sense to detect the presence of seizable objects

Plain Hearing-conversation carried on in the presence of an officer or informant can be lawfully overheard

Plain Shape-containers can be opened where their outward appearance reveals criminal contents

Devallis Rutledge, a former police officer and veteran prosecutor, now serves as Special Counsel to the Los Angeles County District Attorney. His latest book is "Criminal Investigations and Evidence."