"At trial the Government was permitted, over the petitioner's objection, to introduce evidence of the petitioner's end of telephone coversations, overheard by FBI agents who had attached an electronic listening and recording device to the outside of the public telephone booth from which he had placed his calls. In affirming his conviction, the Court of Appeals rejected the contention that the recordings had been obtained in violation of the Fourth Amendment, because ‘(t)here was no physical entrance into the area occupied by, (the petitioner).’"
"We conclude that . . . [t]he Government's activities in electronically listening to and recording the petitioner's words violated the privacy upon which he justifiably relied while using the telephone booth and thus constituted a ‘search and seizure’ within the meaning of the Fourth Amendment. The fact that the electronic device employed to achieve that end did not happen to penetrate the wall of the booth can have no constitutional significance."
"Because the surveillance [occurred without an advance judicial warrant], and because it led to the petitioner's conviction, the judgment must be reversed."