If your car alarm is triggered you may want it to make a lot of noise.
One of the most effective ways of doing this is to add horn honk to your car alarm. This simple installation technique hooks your car horn up to the alarm so if the alarm is triggered the horn will sound at the same time as the siren.
This only happens when the alarm is triggered, not when you arm and disarm the alarm.
Horn honk is a cost effective upgrade for any car alarm system. Another option is to add a screamer siren.