Hong Kong has a reputation for being a safe place. Any modern aid to effective law enforcement that helps our police keep it that way is to be welcomed, as long as respect is shown for the rights and freedoms we value just as much as our safety.

An imminent trial of body cameras, which enable officers to film with sound while on active duty at 'major incidents' such as protests, will therefore be of interest to human rights groups as well as police management. The use of video cameras under the direction of senior officers to monitor the city's increasingly frequent mass protests is not new. What sets these new, cigarette-pack sized, lapel-mounted cameras apart is the ability to film face-to-face encounters, and the delegation of discretion to individual officers about when to turn them on - and off. If the result of the trial is favourable, the police force is said to be ready to order up to 7,000 of them. British and US police forces have used them widely for years, and one Scottish force swears by them, claiming that they have led to earlier guilty pleas, raised the success rate of prosecutions and left officers with more time for community policing. Elsewhere there have been privacy concerns, with two of Australia's state police forces having declined to adopt them widely and the largest having no plans even to test them.

Hong Kong has a reputation for peaceful protest. But the decision to test body cameras follows controversy over claims of over-zealous policing of demonstrations. A police source says body cameras will be a deterrent not only to would-be offenders but also to police over-reaction. Indeed, police chief Andy Tsang Wai-hung says they will be mutually beneficial and plays down privacy fears. But if abused for identification and unauthorised surveillance, they do have the potential to violate privacy and impinge on the right to protest. That would endanger essential trust between police and public. If adopted for general use, this must be under strict and transparent guidelines.