ATO is a tradename based on Hatot
In "Horologerie Electrique" it is noted that Leon Hatot was sucessor to Paul Garnier of Paris.
Marius Lavet, who had been closely associated with Favre-Bulle, was a graduate of the Art et Metiers and l'Ecole Superioure d'Electricite, Paris and became a Professor of l'Ecole Nationale Supoericure de l'Aeronautique, Paris.
In 1922 he published his notes on electrical timekeeping.
In the same year Hatot produced prototypes of their battery electric clock based on M. Lavet's designs, and also in that year M. Lavet became a director of Etablissement Leon Hatot et Cie.
Lavet took out a patent in 1953 for a clock which incorporated transistors and these appeared on the market in 1955. This is the first known use of transistors being utilised as a switch in a clock and had the big advantage of avoiding the use of a mechanical contact.
The Leon Hatot company later licensed other companies to make clocks to this design
It appears that ATO continued continued to make clocks until at least 1948. HAC, one of the licensees, made them from 1928 to 1932, and following the takeover of HAC by Junghans they continued to be made by that firm until 1962