“Nearly everybody’s got the same doorbell / The bronze clapper’s almost gone by the board / I’ve half a mind to invent something / instead of the doorbell”. Bruno Munari and Davide Mosconi applied structures and machines producing the most strange and different sounds to a series of doors “instead of the ringing doorbell”. Sounds are related with the imaginary owner of the door: for example ringing at Pietro di Pietra the geologist’s door means using a knocker on a stone. These doors were shown in 1991 at the Danese showroom in Milan and are shown again in Lualdi Porte showroom for Bruno Munari’s birth centenary.