Although the vehicle horn is a minimal audible unit for communication, we will show that its uses are impressively varied. Drawing upon a corpus of video recordings from dashcams, we show how drivers use the horn for creating awareness; how they target particular vehicles; and how they use it for warnings, for complaints, and in instructing the seeing of an aspect of an ambiguous traffic object. Drivers' use of the horn involves, first, their sounding it in recognizable relations to past, current, and projected configurations of traffic on the road. Second, it involves drivers manipulating the vehicle horn to create sounds of shorter and longer durations that can then produce hearably distinct actions. Third, and finally, the driver can use the horn as an initiating or responsive action in relation to the actions of other members of traffic. The data are from road users in Chennai, India.