S. Siedle & Söhne Telefon- und Telegrafenwerke OHG is a

a leading manufacturer of building communication technologies. They make a range of of audio & video intercoms, video intercom systems, access control and security systems. In 1935, Siedle created its “Portavox”, the first door loudspeaker.

Furtwangen, Germany
founded 1750
http://www.siedle.com/