backup siren basic help

I'm wanting to add a couple backup sirens to my alarm.  How do you guys usually go about hooking them up?  How do they work (how does it connect?) and what type do you recommend?  The DEI with the built in backup battery and key in the back?

I have one of these in my truck and its about 10 years old. Still works great (I think). It has 4 wires to it. power (constant) ground trigger (-) trigger (+) I tested mine when it was like 5 years old by unplugging it (while in the truck) it went off for about 10 minutes without any real noticable difference in sound. It actaully has a huge capacitor in it and not a battery (at least the one I had which sounds the same). I hooked it up in the engine bay where it could be seen (cause I used all of the hiding places on the regular sirens) and made it so the trigger wire was buried and tie strapped really good and left the positive (constant) more visible and easier to get to. I figured this way they a thief would reach in and cut the 1st wire he saw. That wire being power the siren would then never shut off. p.s. remember to turn them off when you take the truck to be serviced!

Thanks for the reply.  So the positive or negative trigger gets hooked up to the alarms's siren output depending on the alarm (positive in my case since it's a DEI alarm)?

yup

If you really want to make sure that it doesnt get ripped and you are installing this in a truck. Lower your spare tire and mount it to the frame/bed between the tire and bed. Really had to get through that way. You just have hide the wires really well so it's to much trouble to find and cut.