The warning was a false alarm—one of the satellites had misinterpreted the glint of sunlight off clouds near Montana as a missile launch—but to the Soviets, it appeared the United States had started a nuclear war.
Protocol demanded that Serpukhov-15 report any signs of a missile launch to the Soviet high command, but Petrov had a hunch the warning was an error. He knew the new satellite system was mistake-prone, and he also reasoned that any nuclear strike by the Americans would come in the form of hundreds of missiles, not just five.
With only minutes to make a decision, Petrov chose to ignore the blaring warning alarms and reported the launch as a false alarm—a move that may have averted a nuclear holocaust.
The incident remained classified until after the Cold War ended, but Petrov later received several humanitarian awards for his extraordinary actions, and was even honored by the United Nations.