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Avant garde composer George Antheil, a son of German immigrants and neighbor of Lamarr, had experimented with automated control of instruments. Together, they submitted the idea of a Secret Communication System in June 1941. On 11 August 1942, U.S. Patent 2,292,387 was granted to Antheil and Hedy Kiesler Markey. This early version of frequency hopping used a piano roll to change between 88 frequencies and was intended to make radio-guided torpedoes harder for enemies to detect or jam.

The idea was impractical, ahead of its time, and not feasible due to the state of mechanical technology in 1942. It was not implemented in the USA until 1962, when it was used by U.S. military ships during a blockade of Cuba,[4] after the patent had expired. Neither Lamarr nor Antheil (who died in 1959) made any money from the patent. Perhaps due to this lag in development, the patent was little-known until 1997, when the Electronic Frontier Foundation gave Lamarr an award for this contribution.[1]

Lamarr's and Antheil's frequency-hopping idea serves as a basis for modern spread-spectrum communication technology used in devices ranging from cordless telephones to WiFi Internet connections, namely CDMA.[5] Similar patents had been granted to others earlier, like in Germany in 1935 to Telefunken engineers Paul Kotowski and Kurt Dannehl who also received U.S. Patent 2,158,662 and U.S. Patent 2,211,132 in 1939 and 1940.

Lamarr wanted to join the National Inventors Council, but she was told that she could better help the war effort by using her celebrity status to sell War Bonds. She once raised $7,000,000 at just one event.