The Mikiphone, via We Make Money Not Art:
Patented in 1924, it could fold up to the size of a large pocket watch. All the parts --apart from the winding handle-- are stored inside the case which when closed has a diameter of just 4½" (11.5 cm) by under 2" thick (4.7 cm). The 'horn' is in two parts and can be stored inside the case. Le Corbusier said that the Mikiphone was the essence of the esprit nouveau.