Does anyone know, What is the brand of this smoke detector?
That is a Detection Systems DS200HD commercial photoelectric smoke/heat detector, mounted on either a 2-wire MB200-2W or 4-wire MB200-4W base, all of which were supposedly made back in the 80s (don’t know exact manufacturing dates though). I have two DS200s & two MB200-2Ws, the former of which are the same as the DS200HD but without a heat sensor (thus meaning they’re just smoke detectors). All in all, they are very rare detectors & detector bases indeed: I’ve only spotted them in a handful of places.