A sex workers' concern group is developing a system that allows prostitutes to keep in touch with each other when they are with a client. Elaine Lam Yee-ling, spokeswoman for the Zi Teng NGO, said it had tried to contact as many prostitutes as possible who operate one-woman brothels after they learned about the first murder. 'We want them to join our communication network so that they can call one of the sex workers in the network before and after serving customers. Then we can make sure that these sex workers who work alone are safe and sound,' she said. 'We also have outreach teams to contact sex workers and invite them to join our network for the sake of their safety.' Miss Lam said there were about 3,000 one-woman brothels in the city, and about 700 of them had already joined the scheme. 'Most of these sex workers who work alone are quite isolated. We will try to reach out to them and persuade them to join our network. We appeal to all sex workers to call us and join our network as soon as possible so that they can look after each other.' Miss Lam said sex workers in the network also shared intelligence among themselves. 'The workers can spread messages and information about the recent killings, which is important for their safety as they can reject customers who look suspicious. 'Experienced workers can offer tips and help those who have just joined the industry.' The group will also organise training courses such as self-defence combat techniques and first aid. 'We hope sex workers can equip themselves with some combat skills and can defend themselves when being attacked.' Miss Lam said some prostitutes had installed closed-circuit television cameras at their brothels, but sometimes the wires or cables had been cut by police officers when they were carrying out operations, or by technicians. Action for Reach Out, another concern group, said the sex industry was studying the possibility of setting up an emergency link under which an alarm would be installed at every one-woman brothel and they could press the alarm for help when in danger. The group has set up a 24-hour hotline for sex workers. The group is also organising a class in Chinese martial arts for sex workers next month. As a further security measure, a website in which one of the victims put up an advertisement for her one-woman brothel was taken down yesterday afternoon. 'Since there are some serious crimes that have happened in Hong Kong recently, we decided to stop our service temporarily,' a message posted on the website said.