Found this interesting...
http://www.kickstarter.com/projects/153591688/banshee-horn-safety-system-for-motorcycles-cars-an"...The electronics in this product control the loud air horn and the high beam lights. If you press the horn switch briefly, only the regular horn is activated. Pressing the switch for ½ second causes the logic in the control unit to now engage the raucous air horn (135 decibel) and high beam lights. When doing this, it pulses both the horn and lights for even greater impact - as shown in the video.
When designing the electronics we paid particular attention to safety. We do not in any way alter the regular horn system in the motorcycle or car to keep within DOT (Dept of Transportation) regulations.
Also, we don’t put any electrical loads on the existing vehicle wiring because we take our power directly from the battery.
The Banshee Horn system has been patented to cover all types of motor vehicles including several design forms and iterations..."