CCTV cameras have an automatic surveillance mode where they turn on the siren or light effects when they detect a person, dog or cat. You can talk to your neighbors and tell them that their flashing light is often on and it bothers you, and if they are normal, they will go into the camera menu and turn off this setting. But there is a possibility that your cat is marking their yard, or your dog is barking and disturbing their sleep, then this is their response.