For years I wondered just what happened to ESL, also known as “Electro Signal Lab”, maker of both residential & commercial smoke detectors & rebrander of commercial pull stations such as RSG’s RMS-1T. At first I assumed they had gone out of business since I couldn’t seem to find a trace of them anywhere online; they didn’t even appear to have an official website; eventually I determined that much like how “First Alert” is a brand name used by BRK Brands Inc, “ESL” is actually a brand name once used by a company named “Sentrol Inc.”. When it comes to the latter it seems they were acquired by GE around the early 2000s. Not sure what became of them & ESL after that.