"Ding ding" - it's a sound that is part of the lives of many Hongkongers, but for Yip Won-cheong and Ko Lai-bing, it resonates much deeper.
Yip, 65, has worked for Hong Kong Tramways for 40 years, and is now its longest-serving employee.
Ko, 59, has been a tram driver for 25 years. Late British prime minister Margaret Thatcher and former governor Chris Patten have been among her passengers.
As the company celebrated its 110th anniversary yesterday, the pair relived some of their memories, including the early days when fleas used to bite the drivers.
Yip's parents and brother also worked on the trams. Yip had been a construction worker and shopkeeper before signing up to Tramways.
"But my joining had nothing to do with my family [working there]," said Yip. "I met an uncle one day on a tram, and he introduced me to the company. My father didn't know I had joined the same company before I started work."
Yip started as a driver, but became an inspector after seven years. He has also trained drivers and is now a senior inspector.
Ko was a housewife before becoming a tram driver. She said the training required a lot of strength because they had to practise moving the overhead cable.
"The actual driving in the past could be exhausting as well, as the steering shaft was hard to move," she added. "Now it's much better. It's like piloting a plane," she said.
When Thatcher visited Hong Kong in 1993, she and Patten boarded Ko's tram.
"I could see why people called [Thatcher] 'the Iron Lady'. She had that cool disposition; she didn't even look at me. I wanted to say 'Hi' but I couldn't," said Ko.
"However, Patten was much nicer. He nodded to me, and I said 'Morning' to him."
Another observation that has left a lasting impression on Ko was that people appeared to prefer taking the tram over other public transport when Sars hit in 2003. "Passengers told me that the air in the tram was fresher because we don't have air conditioners."
It remained a popular form of transport for commuters, despite being viewed as a slower means of travelling, said Ko.
There were only 26 single-decker trams when Tramways was established in 1904. Now, there are 163 trams, and the growth has been vertical, too, with all today's trams double-deckers. When Ko and Yip started in the company, trams were made of wood; today they are of aluminium.
"The floor was uneven, and I would get bitten by the fleas in the driver's cab," Ko said.
To celebrate its anniversary, Tramways is installing screens showing historical footage of the city in 30 trams and will turn its Whitty Street depot into a cinema. Three outdoor film screenings will be held there.