I made a video presentation about this for a school project... regrettably the file no longer exists but it described the political situation at the time and the false alarm that went off in Colonel Petrov's headquarters.
I followed that up with a "Here's what would have happened if Petrov reported the alarms to the defense ministry" and showed (declassified) footage of various Russian and American ICBMs being launched.
Basically on September 26th, 1983 Petrov was on duty at a headquarters of the Soviet air defense forces (similar to NORAD) and was the ranking officer. Around 1 AM local time, he got a warning from the satellite-based launch detection system that a ballistic missile has been launched from the US on a trajectory towards the Soviet Union. He immediately dismissed the alarm as false, because a first-strike by the US was expected to have involved hundreds of missiles, not just one. However, a few minutes later, he received another warning and then another and several more after that, indicating a total of five missile launches. The computer display was flashing the words "START" indicating that the Strategic Rocket Forces were to launch a full retaliatory strike.
Petrov did not contact his superiors and held off, waiting until the missiles were detected on ground radar. When none appeared, he informed his superiors of a computer glitch and false alarm.
Considering the fact that Soviet policy at the time was "launch on warning" (without waiting for radar detection), it is very likely that he averted nuclear war.
Especially since 1983 was an extremely dangerous time and NATO was already running Able Archer '83 which KGB suspected to have been a cover for a surprise nuclear strike.