It would be interesting to see a video of an early SA120 with a squealer horn. Im also thinking since the SA76R pictured here had to have been some kind of rare detector or a variant. Also too if this was 1979 wouldn’t it have still been the SA76RS (squealer horn) and not an RC? Again both detectors appeared a year later in 1980 but since the ad is from December 1979 they could have been early models for 1980 if that makes sense. I have never seen an RC with 8 vents either so definitely again rare but I didn’t think smokes had piezos yet in 1979. None that I heard back then did, only squealers.