Perth police will be fitted with body cameras in a six-month trial from February 2016.

Officers in Perth metro response teams, local policing teams, traffic and the regional operations group will be fitted with the cameras, and it will be compulsory for them to be used.

In a statement, WA Police said the cameras would protect members of the community and police officers.

"The connection between BWV [body worn video] and crime reduction/officer safety relates to the theory of socio-cognitive behaviour," the statement said.

"In social contexts, knowing that one is being observed leads to modifications of behaviour and often into socially-desirable responses.

"Anyone with a smart phone can now record video footage of a police encounter.

"Body-worn cameras ensure events are also captured from an officer's perspective."

Police hope the cameras will lead to increased early guilty pleas, reduce the need for use of force by officers, reduce false complaints against police, improve police legitimacy and improve behaviours for police and the community.

Officers will have a pre-prepared script to let people know they are being filmed.

Some video to be stored for years

Police Commissioner Karl O'Callaghan said many police maintained complaints made against them had been made unfairly, and the cameras would help speed up investigations into such matters.

Mr O'Callaghan said while most video captured through the cameras would only be stored for a specific period, vision from officers involved in significant or serious incidents would be held on file.

"Obviously, more major incidents, incidents which are likely to be controversial or may result in a protracted complaint investigation will be kept for a number of years," he said.

The video will not be accessible to officers.

Mr O'Callaghan said he expected a successful trial would result in a force-wide implementation of body cameras.

"I think what we will see is a complete roll out of cameras to all operational officers probably by the following year [2017]," he said.

The trial groups' outcomes will be compared to groups without the cameras.