監視カメラ
The earliest form of pay-per-view was closed-circuit television, also known as theatre television, where professional boxing telecasts were broadcast live to a select a number of venues, mostly theaters, where viewers paid for tickets to watch the fight live. The first fight with a closed-circuit telecast was Joe Louis vs. Jersey Joe Walcott in 1948. Closed-circuit telecasts peaked in popularity with Muhammad Ali in the 1960s and 1970s, with "The Rumble in the Jungle" fight drawing 50million buys worldwide in 1974, and the "Thrilla in Manila" drawing 100million buys worldwide in 1975. Closed-circuit television was gradually replaced by pay-per-view home television in the 1980s and 1990s.