Started in 2005, World  Inventors’ Day is mainly celebrated in Germany, Austria and Switzerland on Nov 9. It honors the birth of Austrian actress and inventor Hedy Lamarr, born on Nov 9, 1914. During World War II, she and the US composer George Antheil developed a “secret communication system” to help guide torpedoes (鱼雷) by radio. The system allowed a ship and its torpedo to change radio frequencies (频率) together in a set pattern, making it harder for enemies to block their signals. This idea is called frequency hopping (跳频). It laid the groundwork for many modern technologies, including Wi-Fi, GPS and Bluetooth.