Plain Feel Search
In Minnesota v. Dickerson, 508 U.S. 366 (1993), the Supreme Court recognized a "plain feel" corollary to the "plain view" doctrine.
When "a police officer lawfully pats down a suspect's outer clothing and feels an object whose contour or mass makes its identity immediately apparent, there has been no invasion of the suspect's privacy beyond that already authorized by the officer's search for weapons; if the object is contraband, its warrantless seizure would be justified . . . ." Id. 375-376.
However, the Supreme Court affirmed the lower court's decision that the specific officer conducting a pat-down on Dickerson did not obtain a plain enough feel to have probable cause to believe that the substance in his pocket was contraband. Id. 379.