Police Commissioner Andy Tsang Wai-hung tried to play down fears about a controversial scheme to fit officers in the tactical and emergency units with body-cameras.
He said only behaviour that breached the law and public order during protests would be filmed in the proposed trial.
News of the scheme has led to privacy fears.
Speaking after a Junior Police Call event, Tsang tried to reassure the public that officers would not film their targets secretly and added that the person being filmed would know the camera was being used because the screen faces outwards.
'When the device is filming, the targets will know that they are being filmed. It is not a secret filming situation,' he said. He added that the trial would start in the next few months.
He reiterated that the trial was not targeting peaceful demonstrations, but illegal behaviour during protests that breached the public order.
He said this was being done at present with the use of hand-held cameras. 'It is beneficial to both [police and protesters]. Facts speak louder than words.
'Very often now we do not have good means of recording [evidence]. It would be unfair to both parties when there is any misunderstanding and untrue statements.'
He said officers would need to seek authorisation when operating the cameras, and footage would be deleted after fulfilling its purpose.
Law Yuk-kai, director of Hong Kong Human Rights Monitor, said the Basic Law protected people from being monitored by the government and law enforcers.
'When a person protests, it does not mean he is willing to be filmed. Even when he is willing to be filmed by the media, it does not mean he is willing to be filmed by the police.'
He said there should be public consultation before any trial.