Lamarr's earliest inventions include an improved traffic stoplight and a tablet that would dissolve in water to create a carbonated drink. The beverage was unsuccessful; Lamarr herself said it tasted like Alka-Seltzer. With the ongoing World War, Lamarr was inspired to contribute to the war effort, designing a jam-proof radio guidance system for torpedoes. With the help of composer George Antheil, they drafted designs for a new frequency-hopping, spread-spectrum technology that they later patented.
Lamarr and Antheil realized that radio-controlled torpedoes, which could be important in the naval war, could easily be jammed, thereby causing the torpedo to go off course. With the knowledge she had gained about torpedoes from her first husband, and using a method similar to the way piano rolls work, they designed a frequency-hopping system that would continually change the radio signals sent to the torpedo.
Their invention was granted a patent on 11 August 1942 (filed using her married name Hedy Kiesler Markey). Yet, it was technologically difficult to implement, and the U.S. Navy was not receptive to considering inventions coming from outside the military at the time. Only in 1962, at the time of the Cuban missile crisis, did an updated version of their design appear on Navy ships. The design is one of the important elements behind today's SPread-spectrum communication technology, such as GPS, CDMA, Wi-Fi networks and Bluetooth technology.
They eventually received the Electronic Frontier Foundation Pioneer Award and the Bulbie Gnass Spirit of Achievement Bronze Award, given to individuals whose creative lifetime achievements in the arts, sciences, business, or invention fields have significantly contributed to society. Lamarr was also featured on the Science Channel and the Discovery Channel. In 2014, Lamarr and Antheil were posthumously inducted into the National Inventors Hall of Fame.