the system is called "perimetr," and a lot of people have rather silly ideas about it; what was actually built (the soviets did some odd things, but they weren't insane or irrational about these things) wasn't, in the end, all that different from the arrangements the us made to ensure command and control of the nuclear forces. the actual perimetr system was, if memory serves, never intended to operate completely automatically. what it would do is that, if some officers in a special bunker monitoring certain systems had reason to believe a nuclear strike had occurred, they'd launch special communications missiles - these were modified icbms with special payloads - that would rise into the sky and transmit a message to launch the force to the land-based soviet nuclear forces. in a way it wasn't too dissimilar to what the brits have arranged with letters of last resort; according to e.g. the wikipedia article on the same, the skippers of british nuclear submarines are apparently supposed to make certain checks to see if there is evidence of there having had been a nuclear strike on britain, and if there is evidence that britain has been annihilated in a nuclear strike, the letter might instruct them to launch their weapons. such an event wouldn't occur out of the blue anyway.   you're thinking of what happened with stanislav petrov. that didn't have anything to do with perimetr directly; rather, it had to do with this soviet satellite system, the equivalent of the american dsp, falsely detecting an icbm attack - apparently, it mistook sunlight gleaming off cloud formations over the midwest for the glare of rocket motors. theodore postol talked about the technical aspects of this in a video lecture, but i can't dredge it up at the moment.
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