Sunday Communications has launched a service that allows users to be tracked via their mobile phones. The new service, following on from a Sunday service that allowed users to pinpoint the location of Sars-affected buildings, will enable local mobile users to know the location of registered customers. The smallest mobile operator in Hong Kong said its Family Watch service was aimed at family members wanting to keep track of each other, a growing concern because of the threat of Sars. To avoid compromising users' privacy, Sunday said customers interested in utilising the service would be required to give their authorisation to designated callers. The service, available only in Hong Kong, is capable of providing location information, at the street and district level, to within 200 metres to 500 metres of the receiver, through a short message service. It can show information as detailed as the food court in Times Square, or a particular MTR station. Sunday group managing director Bruce Hicks said: 'It really has been the attention on Sars that brought to us the importance of a location-based service. I would expect more location-based services to be launched in the near future.' Mr Hicks said Sunday had provided a similar location-based service to Hong Kong and China Gas for the past three years that kept track of service representatives. Last month, Sunday became the first mobile operator to launch a service that provided information about infected buildings within a kilometre of the caller's location. Users are billed a minute of calling time for the service and Mr Hicks said 3,000 callers were using it a day. The operator says it hopes the new service will help offset part of the revenue losses suffered by mobile operators in Hong Kong because of the ongoing Sars outbreak. Mr Hicks admitted that mobile roaming inbound traffic had fallen 60 per cent, with outbound traffic to China down 20 per cent in the past month because fewer people were travelling.