Is there a technique or a device you can add to an alarm system that sounds the car horn in random pulses whent he alarm is triggered?

a relay hooked up to your flashing lights would do it. However if your alarm requires a relay to flash your lights, then you could tap into that. But a built in lights relay I would not trust, and would wire in an external more robust one just in case for piece of mind.

but that won't randomly make the horn honk different lenghts of pulses right? Like a 1 sec beep then a 2 second beep then a 1 sec beep...etc..

if you don't diode isolate the alarm's parking light output, turning your parking lights on will activate your horns.

most aftermarket alarm sirens pulse out for arm/disarm notification and constant for violation notification. you can wire up a 12volt relay and the 12volt output to a 12volt flasher. the flasher can pulse the horns accordingly.

unless the alarm is an older clifford g3 where it has a seperate horn output.

netZ

a relay hooked up to your flashing lights would do it. However if your alarm requires a relay to flash your lights, then you could tap into that. But a built in lights relay I would not trust, and would wire in an external more robust one just in case for piece of mind.

you can just use a regular relay with pretty much any alarm.. what we usually do is use the dome light supervision as the ground input for the relay, and use the siren output as the 12 volt input for the relay.. that way it will pulse the horn when the alarm is in panic mode....... or you can use a couple of diodes and use the parking light output......