There is a ute/ small truck running around Blackwater Qld with a set of 5 klaxons mounted on the roof of the cab.
I have 4 decent sized chromed steel air horns behind the grill of the Nissan, running off an air tank charged to about 120psi. Its a great prank when I get the car serviced, the guys that know they are there will get a newbie to check the horn. They usually smeg themselves. They are deliberately LOUD, so if someone driving their car, with AC on, stereo blaring, ect, can still hear me.