Got this very interesting trio of white NIB Simplex 4903-9423 Horn/Strobes rated for 30 CD (110 on-axis). These have sync only strobes and have the older electronic horns on them. The 4903-9423 is supposed to be a red horizontal sync model. However, I guess Simplex made some of these with a white housing as a special order sort of thing, hence probably why there is no label on the back of the strobe housing. These rectangular 4903s are my favorite wall mount notification appliances (especially in white) and I am more than happy to add them to my collection.
I would be happy to hear discussion on other members thoughts of these units or answer any questions!
