Why is my dog doing this?

So we have this carbon mynoxide detector in the wall, and I took it out and put it back in. When I did it made a beep noise, and my dog came running to the detector in the wall, and starting scratching it and the wall. I did it again and he repeated his actions but also scratching at the floor. He tilts his head in confusion and I'm wondering is it hurting his ears or is he just curious about the noise.