FBI attaches listening device to outside of a Los Angeles phone booth used by Charles Katz to place illegal bets, bypassing the warrant requirement by claiming no physical intrusion occurred

FBI agents investigating Charles Katz for interstate transmission of wagering information attached an electronic listening device to the outside of a public telephone booth in Los Angeles that Katz regularly used to call bookmakers in Miami and Boston. Agents made recordings without obtaining a warrant, reasoning that the 4th Amendment required only that they refrain from physically entering a constitutionally protected space — and since the device touched only the outside of a public booth, no intrusion had occurred. Katz was indicted on eight counts of interstate transmission of betting information based entirely on the recordings.