This 1979 movie is based on a book that supposedly tells the true story of the Lutz family and the horrific paranormal experiences they endure after moving into a house where brutal murders had occurred. It's since been revealed that the Lutz story was a hoax, albeit a successful one considering the money made from book and film rights.
The details of the Amityville haunting are countless and lurid, but what we really care about is Harry the dog. Did the demon/Native American spirits involved do him any harm? He certainly seems disturbed by the hidden room the family uncovers in the basement, cowering and refusing to go near it. But when the haunting gets to be too much and the Lutz family flees at the end of the movie, Harry is with them, safe and sound.