The makers of the smart video doorbell Ring have entered into a partnership with four hundred American police forces. This allows the forces to request images from millions of users' cameras, The Washington Post writes Wednesday.

The collaboration enables the police to request images of ring cameras in people's homes after a crime. This is possible based on a specific period or area.

Agents do not get access to live images. The police can request permission via e-mail. Owners can accept or reject the request.

Ring cameras record images when motion is detected via the sensors. The company is part of tech giant Amazon.

Ring and the police forces see the camera network as a way to keep neighborhoods safer and to assist with police investigations.

Privacy groups and lawyers are more reserved, writes The Washington Post . For example, civil rights could be at stake and citizens may turn into informers.