Yasmin Subba, 16, Sha Tin College

My initial reaction would be, "This is amazing!". I'd love to get a laugh scaring people by moving their stuff around, loudly playing the piano, or writing, "I'm watching you" on a whiteboard.

After that, I'd just have to go in all the doors that say "No Entry" or "Staff Only" just to see what's so important inside. Yet invisibility isn't a power everyone can use properly; it can easily be used for unethical ends. For example, what would happen if someone found out about my invisibility and forced me to steal?

I really like attention, so I'd enjoy my invisibility for one day, but would be happy to be me again the next day.

Thichachon Jaipakdee, 17, St Paul's Convent School

I would be saved from the humiliation of anything I have caused in the past. I would get rid of the humdrum parts of my life and enjoy roaming around like a free, delighted bird. I would become invisible so I could know the unknown mysteries of the world.

I would eagerly examine the roles played by secret government agencies, such as the FBI and CIA, by entering their headquarters without detection, despite the tight security in place. Then I could learn the secrets of everything and everyone.

Zareen Chiba, 18, Li Po Chun United World College of Hong Kong

Passing through Hong Kong immigration at Chek Lap Kok would be a breeze, so I'd hop on a two- or three-hour flight to places such as Vietnam or Laos and soak up the local atmosphere.

I'd go to the liveliest market and leave a few dollars while treating myself to food from a stall. Or I'd sit on a public bus, or on the back of a motorcycle, and see where it took me. Best of all, being invisible would mean I'd avoid crowds trying to sell me things.

Yet I'd be sure to return to the airport in time for a flight back to the city, so I didn't become visible and - amid much confusion - end up at the local Chinese embassy.

Elise Choi Ho-yee, 18, Sai Kung Sung Tsun Catholic School (Secondary Section)

It depends on what day it would fall. If it fell on April Fool's Day, I'd play tricks on my friends and family, such as tripping them up, or making scary sounds.

I wouldn't feel guilty as you're supposed to play tricks on this day. At the same time, the "victims" wouldn't feel it was strange.

If it fell on Christmas Eve, I'd be an "invisible Santa Claus". I'd steal Christmas presents from stores and put them in the homes of the poor, so their children could share the happiness of this wonderful day.

If it was a normal school day, I'd go to school, even though I'd be marked "absent"; I wouldn't want to miss any lessons so I could keep up with my studies.

Mizuki Nishiyama, 13, Canadian International School

I'd follow my dad in the morning, all the way to his workplace to spy on him. I want to know what he actually does in the office. He deals with a lot of paperwork and I want to see how he handles it all, along with the many conflicts that crop up in the different factories of his company.

First of all, I'd probably lie on top of his desk and fall asleep. Then I'd sneak some food out of the fridge.

At the end of his working day, we'd go home together without him even noticing.

Doris Lam, 15, St Margaret's Co-educational English Secondary and Primary school

I'd sneak into a dermatologist's office and sit and listen to what he has to say to his clients.

I've had acne since I was 10, and have tried so many products, but nothing works for me.

My mum thinks that going to a dermatologist is a waste of money. Hence, sneaking into his office and listening to his advice about how to treat acne would not only save my family money, I would learn a lot ...

Who knows? I might even fall in love with his job.