In the 1940s, few Hollywood actresses were more famous and more famously beautiful than Hedy Lamarr. Yet despite starring in dozens of films and gracing the cover of every Hollywood celebrity magazine, few people knew Hedy was also a gifted inventor. In fact, one of the technologies she co-invented laid a key foundation for future communication systems, including GPS, Bluetooth and Wi-Fi.

“Hedy always felt that people didn't appreciate her for her intelligence—that her beauty got in the way,” says Richard Rhodes, a Pulitzer Prize-winning historian who wrote a biography about Hedy.

After working 12- or 15-hour days at MGM Studios, Hedy would often skip the Hollywood parties or carousing with one of her many suitors and instead sit down at her “inventing table.”

“Hedy had a drafting table and a whole wall full of engineering books. It was a serious hobby,” says Rhodes, author of Hedy's Folly: The Life and Breakthrough Inventions of Hedy Lamarr, the Most Beautiful Woman in the World.

While not a trained engineer or mathematician, Hedy Lamarr was an ingenious problem-solver. Most of her inventions were practical solutions to everyday problems, like a tissue box attachment for depositing used tissues or a glow-in-the-dark dog collar.

It was during World War II, that she developed “frequency hopping,” an invention that’s now recognized as a fundamental technology for secure communications. She didn’t receive credit for the innovation until very late in life.

Hedy Lamarr was born Hedwig Eva Kiesler in Vienna, Austria in 1914. She was the only child of a wealthy secular Jewish family. From her father, a bank director, and her mother, a concert pianist, Hedy received a debutante’s education—ballet classes, piano lessons and equestrian training.

There were signs at a young age that Hedy had an engineer’s natural curiosity. On long walks through the bustling streets of Vienna, Hedy’s father would explain how the streetcars worked and how their electricity was generated at the power plant. At five years old, Hedy took apart a music box and reassembled it piece by piece.

“Hedy did not grow up with any technical education, but she did have this personal connection,” says Rhodes. “She loved her father dearly, so it’s easy to see how from that she might have developed an interest in the subject. And also it prepared her to be what she really was, a kind of amateur inventor.”

Even if Hedy had wanted to be a professional engineer or scientist, that career path wasn’t available to Viennese girls in the 1930s. Instead, teenage Hedy set her sights on the movie industry.

“At 16,” says Rhodes, “Hedy forged a note to her teachers in Vienna saying, ‘My daughter won’t be able to come to school today,’ so she could go down to the biggest movie studio in Europe and walk in the door and say, ‘Hi, I want to be a movie star.’”

Hedy started as a script girl, but quickly earned some walk-on parts. The Austrian director Max Reinhardt took Hedy to Berlin when she starred in a few forgettable films before landing a role at age 18 in a racy film called Ecstasy by the Czech director Gustav Machatý. The film was denounced by Pope Pious XI, banned from Germany and blocked by US Customs authorities for being “dangerously indecent.”

Reinhardt called Hedy “the most beautiful woman in Europe,” and even before Ecstasy, Hedy was turning heads in theater productions across Europe. It was during the Viennese run of a popular play called Sissy that Hedy caught the eye of a wealthy Austrian munitions baron named Fritz Mandl. Hedy and Mandl married in 1933, but the union was stifling from the start. Mandl forced his wife to accompany him as he struck deals with customers, including officials from Nazi Germany and Fascist Italy, including Mussolini himself.

“She would sit at dinner bored out of her mind with discussions of bombs and torpedoes, and yet she was also absorbing it,” says Rhodes. “Of course, nobody asked her any questions. She was supposed to be beautiful and silent. But I think it was through that experience that she developed her considerable knowledge about how torpedo guidance worked.”

In 1937, Hedy fled her unhappy marriage (Mandl was deeply paranoid that Hedy was cheating on him) and also fled Austria, a country aligned with Adolf Hitler’s anti-Jewish policies.

Hedy landed in London, where Louis B. Mayer of MGM Studios was actively buying up the contracts of Jewish actors who could no longer work safely in Europe. Hedy met with Mayer, but refused his lowball offer of $125 a week for an exclusive MGM contract. In a savvy move, Hedy booked passage to the United States on the luxury liner SS Normandie, the same ship on which Mayer was traveling home.

“She made a point of being seen on deck looking beautiful and playing tennis with some of the handsome guys on board,” says Rhodes. “By the time they got to New York, Hedy had cut a much better deal with Mayer”—$500 a week—“with the proviso that she’d learn how to speak English in six months.”

Mayer had another demand—she had to change her name. Hedwig Kiesler was too German-sounding. Mayer’s wife was a fan of 1920s actress Barbara La Marr (who died tragically at 29 years old), so Mayer decided that his new MGM actor would now be known as Hedy Lamarr.

It didn’t take long for Hedy to emerge as a bright new star in Hollywood. Her breakout role was alongside Charles Boyer (another European transplant) in Algiers (1938). From there, the MGM machine put Hedy to work cranking out multiple feature films a year throughout the 1940s.

“Any girl can be glamorous,” Hedy once quipped. “All you have to do is stand still and look stupid.”

As much as Hedy enjoyed her Hollywood stardom, her first love was still tinkering and problem-solving. She found a kindred spirit in Howard Hughes, the film producer and aeronautical engineer. When Hedy shared an idea for a dissolvable tablet that could turn a soldier’s canteen into a soft drink, Hughes lent her a few of his chemists.

But most of Hedy’s work was done at home at her engineering table where she’d sketch designs for creative solutions to practical problems. In addition to the tissue box attachment and the light-up dog collar, Hedy devised a special shower seat for the elderly that swiveled safely out of a bathtub.

“She was an inventor,” says Rhodes. “If you’ve ever been around real inventors, they’re often not people with a particularly deep education. They’re people who think about the world in a certain way. When they find something that doesn’t work right, instead of just swearing or whatever the rest of us do, they figure out how to fix it.”

In 1940, Hedy was distraught by the news coming out of Europe, where the Nazi war machine was steadily gaining territory and German U-boat submarines were wreaking havoc in the Atlantic. This was a far more difficult problem to fix, but Hedy was determined to do her part in the war effort.

The turning point came when Hedy met a man at a dinner party. George Antheil was an avante-garde music composer who lost his brother in the earliest days of the war. Antheil and Hedy were kindred spirits—two brilliant, if unconventional minds dead set on finding a way to defeat Hitler. But how?

That’s when Rhodes thinks Hedy leaned on the knowledge she picked up years earlier during those boring client dinners with her first husband in Vienna.

“She knew about torpedoes,” says Rhodes. “She knew there was a problem aiming torpedoes. If the British could take out German submarines with torpedoes launched from surface ships or airplanes, they might be able to prevent all of this slaughter that was going on.”

The answer was clearly some type of radio-controlled torpedo, but how would they stop the Germans from simply jamming the radio signal? Hedy and Antheil’s creative solution was inspired, Rhodes believes, by their mutual love of the piano.

During their late-night brainstorming sessions, Hedy and Antheil played a musical game. They’d sit down at the piano together, one person would start playing a popular song and the other would see how quickly they could recognize it and start playing along.

It was here, Rhodes thinks, that Hedy and Antheil first happened upon the idea of frequency hopping. If two musicians are playing the same music, they can hop around the keyboard together in perfect sync. However, if someone listening doesn’t know the song, they have no idea what keys will be pressed next. The “signal,” in other words, was hidden in the constantly changing frequencies.

How did this apply to radio-controlled torpedoes? The Germans could easily jam a single radio frequency, but not a constantly changing “symphony” of frequencies.

In his experimental musical compositions, Antheil had written songs for multiple synchronized player pianos. The pianos played in sync because they were fed the same piano rolls—a type of primitive, cut-out paper program—that controlled which keys were played and when. What if he and Hedy could invent a similar method for synchronizing communications between a torpedo and its controller on a nearby ship?

“All you need are two synchronized clocks that start a tape going at the same moment on the ship and inside the torpedo,” says Rhodes. “The signal between the ship and the torpedo would be continuous, even though it was traveling across a new frequency every split second. The effect for anyone trying to jam the signal is that they wouldn’t know where it was from one moment to the next, because it would ‘hopping’ all over the radio.”

It was Hedy who named their clever system “frequency hopping.”

Hedy and Antheil developed their idea with the help of a wartime agency called the National Inventors’ Council, tasked with applying civilian inventions to the war effort. The Council connected Hedy and Antheil with a physicist from the California Institute of Technology who figured out the complex electronics to make it all work.

When their frequency hopping patent was finalized in 1942, Antheil pitched the idea to the U.S. Navy, which was less than receptive.

“What do you want to do, put a player piano in a torpedo? Get out of here!” is how Rhodes describes the Navy’s knee-jerk rejection. It was never given a chance.

Hedy and Antheil’s patent was locked in a safe and labeled “top secret” for the remainder of the war. The two entertainers went back to their day jobs, thinking that was the end of their inventing days. Little did they know that their patent would have a second life.

In the 1950s, the electrical manufacturer Sylvania employed frequency hopping to build a secure system for communicating with submarines. And in the early 1960s, the technology was deployed on U.S. warships to prevent Soviet signal jamming during the Cuban Missile Crisis.

Antheil died in 1959, but Hedy lived on, unaware that her ingenious idea was about to take off in a big way.

When car phones first became popular in the 1970s, carriers used frequency hopping to enable hundreds of callers to share a limited spectrum of radio frequencies. The same technology was rolled out for the earliest cell phone networks.

By the 1990s, frequency hopping was so ubiquitous that it became the technology standard required by the U.S. Federal Communications Commission (FCC) for secure radio communications. That’s why Bluetooth and other essential technologies are based, at their core, on an idea dreamed up by Hedy Lamarr and George Antheil.

“It’s a really deep and fundamental idea,” says Rhodes. “It has broad applications all over the place.”

Over time, Hedy’s Hollywood star fizzled and she retired to Florida, where she continued to tinker with new inventions, including a more “driver-friendly” type of traffic light. It wasn’t until Hedy was in her 80s that a group of engineers realized that the “Hedwig Kiesler Mackay” listed on the frequency hopping patent was none other than the Hollywood legend, Hedy Lamarr.

“Hedy didn’t want money, but she did want recognition,” says Rhodes, “and it really angered her that nobody gave her credit for this important invention. In the 1990s, she finally got an award for her contribution. And Hedy being Hedy, what did she say? ‘Well, it’s about time.’”