What is the story behind Hedy Lamarr’s patents? What exactly did she invent and how did it work? Some of the websites in which I tried to find the answer made it sound like she perhaps made satelite communications and cell phones possible.
What is the Straight Dope on her?
IIRC, she and another person came up with the idea of “jam-proof” communications. By changing the frequency of a signal, and simultaneously re-tuning the receiver, an enemy trying to jam a signal would be unable to.
I think the idea used something similar to player-piano scrolls. A mechanism would play the scrolls (or whatever) in the weapon and the guidance transmitter so that they would be in synch.
Today we call it “frequency hopping”, and I think a modern analog of that technology is used in cell phones. At the time though, I don’t think the Powers That Were really latched onto the idea.
Of course, this is The Straight Dope, and I’m sure someone will be around soon with just that. 
It is called spread spectrum technology. It was designed for use for radio controlled torpedoes. The frequency of the sending (on the sub) and the receiving (on the torpedo) radios would change quickly with both having a synchronized piano roll device playing at the same speed. Thus if the enemy found the frequency, it would change in a few seconds. She hung out with German scientists before coming to America.
AND DAMNIT! IT’S HEDLEY! HEDLEY! – Harvey Korman