Yay Stanislav Petrov, but a few quibbles.

It's important to note that Soviet nuclear readiness in 1983 wasn't great. The generally-accepted figure is that they were 24 hours away from nuclear launch at any given time. This was a great reason to be terrified of the Americans - the Soviets knew that US command and control was about half an hour to an hour from launching a nuclear strike and they simply weren't. It's also important to note that the automated launch detection systems deployed by the Soviet Union were error-prone, unreliable and held in low regard. It took stones to say "I'll bet my life on the fact that the Americans didn't launch a nuclear attack". But it's easier to say "the computer is probably wrong again, it almost always is" than "huh, never seen that signal before."

It's popular these days to argue that Petrov saved the world. We know about the time he stood the alert down; we don't know if there were other times by other people but we know that the Soviets never launched an attack despite the fact that they had an early warning system that egged them on regularly. We also know that the failure of this early warning system was one of the proximate causes for the Soviets to deploy Perimeter so stories like this are more of a mixed bag than popular culture wants you to believe.

And the US delayed the visa of Petrov's son. It didn't deny Petrov's visa because he never applied for one and has been dead six years.