Lektro Guard heat detector (circa 1975)

Hey everyone well this is one of seven very cool acquisitions that I got from James. They arrived yesterday but I wanted to make a video of this unit first. I will make one with all the others hopefully this weekend. James and I couldn't figure out what batteries this uses. But it might run on 2 C cells. That seems to be the only battery that fits but it doesn't show how to position them and I got very little sound out of it. These are fresh C cell batteries I bought today. It's definitely a strange but cool unit and it is plastic as well. If anyone can help me on the actually correct battery if it's not C cells let me know. I have never seen one of these before but regardless it's cool for a collection. It's cover is cool looking too and I believe this is only a heat detector and not a smoke detector. Enjoy the video!!!