As increasing numbers of people use their Octopus cards to make purchases and pay for their journeys around the city, the Octopus system has spread its tentacles to schools.
While several schools have installed the system to help students settle food bills at tuckshops and pay overdue charges at libraries, some have also come up with ingenious ways to make use of the system as a learning tool.
One of these schools is Tsung Tsin Primary School.
The Prince Edward school spent HK$1 million to install the system three years ago.
'Letting children carry cash worries parents. When they need to pay for an activity, say an upcoming picnic, teachers can collect all their cards, like collecting handbooks, and a clerk in the school office ... can beep all the cards on the card-reading machine,' said principal Tam Woon-ling.
'Not only students and parents benefit, our staff would also save the time and trouble caused by counting and storing notes and coins,' said Dr Tam.
And as all study rooms at the school have had the system installed, the smart cards have also become a key to learning.
'After reciting a poem in the English classroom, a student can beep his card at the door and a mark will be added to his English score,' said Dr Tam.
'Giving the correct answer to a question in the maths classroom adds a point to a student's maths chart.
'The 20 students with the highest scores are singled out every week and given a sash to wear at the weekly morning assemblies.
'Our school places a lot of emphasis on rewards as an incentive to boost voluntary learning.
'Recording all the scores on paper, as in the past, was time-wasting and cumbersome.'
But while the system is very convenient, students can cheat.
'A very small number of students will sneak into classrooms and swipe their cards without reciting any English or solving maths problems,' said Dr Tam.
Apart from the problems with cheating, the cards can easily go missing.
'I've lost my Octopus card twice. Cancelling it and getting
a new one involves a lot of paperwork,' said Joyce Hon, a 17-year-old student at South Island School.
The system was installed there in August.
'The card is a handier version of credit cards. Anyone who picks up a lost card can financially harm the cardholder.
'I also rely too much on it and sometimes forget to put cash in my wallet. More than once, I've found myself short of cash [when I'm shopping].
'After my school used the system to do roll-call, I have seen some of my classmates come in late for classes but ask others to swipe their cards for them in the morning.'
While Joyce has found the Octopus a nuisance, others find it saves them money.
'My mum has applied for the Octopus Automatic Add-Value Service for my card. The money I spend using the card is debited to her credit card account,' said Wai Kai-hong, 17 a former student of New Method College.
'I often visit fast food eateries where Octopus is an accepted form of payment, so that I can save up my pocket money.'
According to the Octopus system operators, about 100 local schools have subscribed to the system.
With schools using the system for roll call, facility booking and payment, the beeping sound will become even more common on campus.