There are a few ways you can detect a camera in your car, 1. Look out for indicator lights or sounds. These can be found reflected from the camera lens. 2. You can purchase a cheap LED CCTV Lens and RF detector. They detect according to light reflections and RF based signals. 3. If you want to detect a camera professionally, you can use a non-linear junction detector. However they are expensive and require professionals to operate it.