1991 jeep cherokee, alarm idea

Wiring into the horn will mean that the siren will pulse as, same as when you arm or disarm an alarm because the horn is pulsing, not staying solid.You could put on a latching relay, but would need a way to turn it off otherwise when you honk the horn and flip someone the bird, your sirens will latch on as well.......

Here's what I did. Mount a siren and wire it straight to +. Take the negative and run it to a relay on pin 87a. Pin 30 goes to ground, pin 86 goes out to a latching relay with a + output. Pin 85 is wired to your doorpins, hood pin, gas cap pin :)......any other negative trigger. The latching relay latches on and off with your doorlocks. To improve on this, put another latching relay on the negative line to the siren, causing it to latch when it  gets the negative from the previous relay. Otherwise when someone opens your door then closes it.......the siren will stop.

I don't know what u have for a starter, but if u can then wire these additional sirens etc. into the remote start so you have some control over it.

I gotta get to work, I'll be back with some more later.