The competition is part of InnoTech Month, organised by Hong Kong's Innovation and Technology Commission, to promote the importance of creativity and innovation among youngsters.
The Gertrude Simon Lutheran College students' winning project is a robot that can play table tennis. With an estimated 300 million players, table tennis, or ping pong as it's known in Chinese, is the biggest amateur recreational sport on the mainland.
"We used table tennis because it is a national sports and a very popular game in China," says 18-year-old Sam Mak Wai-lung.
The robot can shoot the ball to the player on the opposite side of the table. There are three levels of difficulty: starting from the robot in a static position, to its changing direction of shots, to the whole machine moving on the tennis table.
"It is a good device for the many single children on the mainland. They can play with the robot on their own," Sam says.
Sam and two teammates spent seven months drafting the concept, testing the different parts, and finally completing the prototype. It was hard work for the students.
"The biggest challenge was to make the sensors work in all kinds of environments," says 17-year-old Tim Yick Chun-ho who was in charge of the computer programming. "Anything, such as different lighting, can affect the sensory device and I had to adjust it every time to make it work."
Joyce Wong Chun-sau, 19, a mainland student studying at the Yuen Long school, says: "It took me a long time to do the research on the models in the market and purchase all the parts within our budget."
She adds: "I was so happy we won, especially because it's the first time I had entered such a big competition."
A team of Form Five girls at Belilios Public School invented something different and practical for Hong Kong families - a smart electrical plug.
The smart plug is a modified unit with an additional circuit containing a current switch and an electromagnet to cut the electrical supply when necessary.
It can also reset after switching itself off and will not damage other appliances in the house. "It's a safety device which can prevent a potential fire when the fuse is overheated or broken," says Katie Mak Hing-man.
Lily Ha Wai-yee says: "The biggest challenge we faced was that we had not studied electricity before making this device."
Snow Luo Li-ying adds: "We stood for hours in the bookstore reading any information we could find in the books. It was a totally different experience [from studying for exams]. We had to really understand what we were doing."
And to the girls, this is the true essence of creativity. "Creativity is to be able to apply what you have learned," says Rachel Chau Kei-wai. "And talking over your ideas and getting feedback from others is very important."
After they decided on a project, they consulted engineers and professionals about their ideas. Some even told them it was too difficult to make, but that did not discourage them.
In October last year, they won the overall championship, among other awards, at the Joint School Science Competition in Hong Kong.
The smart plug and the ping pong robot, along with other inventions, will be on display at the InnoCarnival 2010 from November 6 to 14. The carnival is part of InnoTech Month.
Visit ce.hkfyg.org.hk/itm for details.