I am posting this at the request of Albra, one of our highly respected members and expert in German clocks. The following is a condensation of information found on the website of the Deutsche Gesellschaft für Chronometrie.

Erich Dees, a collector of mechanical alarm clocks, assembled a comprehensive data base to help in identifying the manufacturers of movements of mechanical alarm clocks that are not stamped with the makers trademark. The shape and size of the back plates of the movements is used as the primary search criterion. Currently, the data base includes over 600 movements, from a period covering roughly the years 1880 – 1996. Mainly German models are covered, but some alarm clock movements of foreign manufacturers are included as well.

The link to his work may be at this location.

I am posting this in the event some of our members may have an interest in this aspect of horology.