Abstract: A two-tone signal generator, serving as a horn for automotive vehicles, crises two complementary half-shells whose interior is divided by a common partition into two convoluted wind channels of different length resonating at different frequencies and opening into a common outlet. The inlet to the wind channels comprises a central duct with two lateral branches terminating at a pair of nipples to which a hose from an air blower can be selectively fitted; the junction of the branches with the central duct is an enlarged space containing a freely movable rubber ball which automatically blocks one nipple when air is admitted through the other nipple. The duct communicates with the two wind channels via respective lateral chambers formed in the two half-shells, each chamber being partly closed toward the outside by a lid provided with an eccentric air slot.