She is a freelance model, a part-time businesswoman and a full-time single mum to a 13-year-old with special needs.

Yet, Sergeant Siti Zuraily Zainal still manages to find time to be a volunteer police officer who patrols MRT stations and bus interchanges for eight hours once a week.

For two years, she has been a part of the Volunteer Special Constabulary (VSC) scheme. Like regular police officers, volunteers carry firearms and have arrest powers.

Five years ago, women volunteer officers made up about 20 per cent of the VSC. Today, about 30 per cent of the 1,000-strong VSC are women.

For Sgt Siti, 37, an admiration for the profession began at a young age - her father was a police officer.

"I thought he looked smart and cool in the uniform, and whenever I looked at him, I felt safe," she said.

"When I was a kid, I would also pretend to be a patrolling officer, riding my bicycle and wearing the police cap."

But her self-doubt stopped her from joining the Singapore Police Force.

After working in the food and beverage industry for about six years, she finally plucked up the courage to apply to become a regular police officer two years ago.

But the training to be a full-time police officer required six to nine months of residential training. As she had to look after her son, she eventually decided the job was not suitable for her.

Instead, she later joined the VSC as "the aim and goal are still there, but there is a flexibility of time".

Compared with regular police officers, VSC officers undergo non-residential training at the Home Team Academy twice a week in the evenings for about six months.

"I can still serve my country and also serve my son," she added with a chuckle.

She later chose to join the Public Transport Security Command because her son, who is autistic, loves trains and other forms of transportation.

Besides patrolling public transportation nodes, she is also involved in high-security events, including the North Korea-US summit and Asean Summit last year.

To keep fit, she goes on 2.4km runs three times a week and is often accompanied by her son, who tags along on his skate scooter.

She said of her volunteer role: "To serve your country is a noble job. To me, it is a form of social responsibility. What you give to people, you will get back in return. Who knows, one day I might need someone's help myself.

"As long as I'm still fit and running, I will serve as a volunteer officer," she added.