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TIL about Hedy Lamarr's motivations for co-inventing frequency hopping 
1/many tweeting out the actual text:
In frequency hopping spread spectrum, a transmitter hops from frequency to frequency hundreds of times per second. It is popular for military communication because it makes transmissions hard to detect and next to impossible to jam.
In frequency hopping spread spectrum, a transmitter hops from frequency to frequency hundreds of times per second. It is popular for military communication because it makes transmissions hard to detect and next to impossible to jam.
It also offers good resistance to fading due to signals taking different paths from source to dest and interfering after recombining. Also offers resistance to narrowband interference because the receiver won't be stuck on an impaired frequency for long enough to shut down comms
This robustness makes it useful for crowded parts of the spectrum, such as the ISM bands we will describe shortly. This technique is used commercially, for example, in Bluetooth and older versions of 802.11.
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As a curious footnote, the technique was co-invented by the Austrian-born film star Hedy Lamarr, who was famous for acting in European films in the 30s under her birth name of Hedwig (Hedy) Kiesler.
As a curious footnote, the technique was co-invented by the Austrian-born film star Hedy Lamarr, who was famous for acting in European films in the 30s under her birth name of Hedwig (Hedy) Kiesler.
Her 1st husband was a wealthy armaments manufacturer who told her how easy it was to block the radio signals then used to control torpedoes.
When she discovered that he was selling weapons to Hitler, she was horrified, disguised herself as a maid to escape him, and fled to Hollywood to continue her career as a movie actress. In her spare time, she invented frequency hopping to help the Allied war effort. 
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Her scheme used 88 frequencies, the number of keys (and frequencies) on the piano. For their invention, she and her friend, the musical composer George Antheil, received U.S. patent 2,292,387.
Her scheme used 88 frequencies, the number of keys (and frequencies) on the piano. For their invention, she and her friend, the musical composer George Antheil, received U.S. patent 2,292,387.
They were unable to convince the US Navy their invention had any practical use and never received any royalties. Only years after the patent expired was the technique rediscovered and used in mobile electronic devices rather than for blocking signals to torpedoes during war time
source: Tanenbaum, Andrew S.; Feamster, Nick; Wetherall, David J.. Computer Networks (p. 103).
