Do I need a motion sensor in a room that already has a camera?

Hey there, I just setup and installed part of my Ring Alarm system. It is all going in a small, roughly 300 square foot room. I will have a ring wired camera, and a ring battery camera in the same room. My question is: Do I need to also install a ring motion detector in the same room I already have ring cameras? The reason behind the question being, don't ring cameras have built in motion detecting already?