"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."