Factory alarm with aftermarket siren?

I think your best bet would be to get an add on alarm that you can use with your factory remotes. The way most of those work, is you wire them up so that they arm when you arm your factory alarm, and disarm when you disarm your factory alarm. That way, you can add your siren, a backup siren, even a glas mic and a shock sensor.Even a radar sensor if youd like, that way you alarm will chirp if someone just gets too close to it!

Yeah, I've done the whole aftermarket alarm thing in the past and am just not willing to deal with a proper install and features.  It's more than I really need.  The flashing LED will warn off any of the opportunistic thieves who just want to smash and rummage.  My idea about the battery back up siren is more for the guys who want to take my car to strip it like recently happened to my Integra.  Those guys know how to steal a car and know that you just need to pull the right fuse to disable the factory alarm as well as the ways around aftermarket alarms.  I want to integrate a battery siren into the power connection for the factory alarm so that if that fuse is pulled, there is a less than pleasant noise comming from inside the dash that can't be disabled.  Makes the car much less attractive to a would-be thief and gives me time to load the old 12-guage...  Are there any harness plug-in's like Metra kits that will allow me to tap into the factory alarm's power lead without cutting wires?  Basically I want to be able to unplug any mod I make to the car and have it be in 100% stock condition when I sell.  Thanks.

I removed my factory horn an placed a cop siren in its place. Any siren would would as long as it is one tone not six or more. That would give your factory a siren sound to it. But becareful your car might have two horns, one for the car and one for the factory alarm. If so then you must search the engine compartment for the second one and either disable it or put the siren there. or even have two sirens. Even sounds pretty cool when someone cuts you off then you can just push your horn and youll get a siren instead.

You could try an air horn in your dash instead. My neighbor has one and damn its loud. I dont think i could do anything in a car with something that loud going off.