While number combination locks may be more convenient to use, locksmiths The New Paper spoke to say padlocks offer more security.

Mr Ben Tan of Express Locksmith, who has 13 years of experience, said one can easily "hack" a combination lock.

"You don't always have to get the right combination. There are videos on the Internet that show how you can jam the system with a certain combination, then pull hard on the lock to open it," he said.

A locksmith with 30 years' experience, who wants to be known only as Mr Koon, said: "If you know the technique... it'll take you less than one minute to open the lock."

He added that it's important to get a sturdy lock as some of those he has seen on gym lockers are "so flimsy you can even cut the lock with kitchen scissors".

Both recommended buying locks from established brands such as Yale, Abloy or Globe.