Hard to imagine , holding on my hands are the Mother of All Memovoxes. Reference 3151 & 3150 , these were the very first Memovoxes , Jaeger LeCoultre released. Original adverts from Life Magazine ,1950 and 1951. Translating the patent documents JLC submitted in 1949 , best way to say it is flared lugs , with a purpose. If you look at the last image of both references , the lugs on each watch carry the case back raised not touching the ground , this ensures that the caseback never really rests on your wrist.. allowing for greater alarm resonance of the caliber 489.
Caliber 489 , which being the first alarm caliber from JLC has and still holds an impressive full 46 hour power reserve with the alarm function.