Despite the tight security, the innovative Balinese-decorated spa is doing a brisk trade while giving inmates at the country's biggest women's prison a trade they can turn to after their release.
"I am not afraid at all because I have faith that these prisoners are well trained to serve the customers and our safety is assured here," said Noor Aliza Osman, 45, who was on her second visit to the spa at Kajang Prison.
"It is comfortable here, the prices are reasonable and I don't have to wait too long to get my hair done like at other salons," said the mother of four who was having her hair coloured with henna by 30-year-old prisoner "Farah".
With her hair neatly tied back and dressed in a loose green jacket and trousers, Farah looked like any other beauty therapist, apart from the prisoner identification number sewn onto her uniform.
"I am very glad to have this chance and I have regular customers here who have been kind enough to ask me to work for them once I am released, as they have become familiar with me," she said with a smile.
"This is a very good experience and I have learned useful skills here. I'm considering opening up my own spa if I have enough money when I am freed."
Farah -- using an assumed name at the request of prison authorities -- is an Indonesian citizen who worked as a waitress before overstaying her visa in Malaysia and being sentenced to one year in jail.
She is among seven prisoners currently working at the spa, who go through four security checkpoints each morning to reach the salon from their cells a few hundred metres (yards) away.
Once at the cosy building, where the scent of aromatic oils floats in the air, they are permitted to mingle freely with their customers, chatting and laughing as they work a nine-hour shift under close watch by three wardens.
Only inmates who have not committed serious or violent offences are considered for a position at the spa. Some 60 percent of the jail's 1,600 inmates are foreigners, many of them Indonesians convicted on immigration charges.
The salon has welcomed a steady stream of customers since opening late last year, offering head-to-toe beauty services such as facials, pedicures, foot reflexology and massages for as little as 30 ringgit (8.5 dollars).
"The response has been overwhelming so far," said the prison's chief inspector Fauziah Husaini.
"Many customers were hesitant to come to a prison at the beginning but ... this programme can change public perception about prisoners so they will be easily accepted by the society in future," she said.
Prisoners working in the spa are paid a small allowance, and the rest of the income generated from the business is used to help fund other rehabilitation programmes, such as bakery and sewing classes.
"We are basically helping them to prepare themselves to adapt to society once again when they are freed. We also hope this programme can lift the veil of secrecy about prison in the eyes of the public," Fauziah said.
"It's all about empowerment and to give these prisoners a sense of confidence, that's how the idea of setting up this spa came about."