You’re looking at the key reset and flag, not the button, which is a large button on the side, which moves VERY easily.Seems an odd way to trigger a panic system. I would expect something much easier to trigger. Could you remove the screw in the middle, take the cover plate and take another photo of the internals? The knob above the red light, looks like a slider type volume control, can it be moved?
The style to me, suggests 1960's.