How do i use this relay?

I want to hook up some more sirens to my car alarm and a backup battery.   My car has a factory alarm with a siren already.  I figured i should hook the relay up to the power sorce of the factory siren and use it as a trigger for my other sirens to go on.  How should i hook up a relay for this?  I have a SPDT Relay .

just hook the new sirens in parallel. don't worry about a relay

as for backup battery. a nine volt usually works use use some diodes (it might be a good idea to run a couple in parallel instead of just one if ur using multiple sirens.

sorry, didn't look like the last pic loaded.

here:

  http://roshfe.com/pulsarnx/scripts/xfer/Docs/Teh_Rox0rz_Carz0rz/siren.JPG

but if u are worried about current draw (if the factory siren is wired straight into alarm "brain" without relay) you will want to use a relay. a simple automotive relay will work

http://roshfe.com/pulsarnx/scripts/xfer/Docs/Teh_Rox0rz_Carz0rz/siren_with_relay.JPG 

sorry, I just looked at that diagram again. It wouldn't work.

(I designed and built my own system from the ground up, and it's wired a little different than factory stuff and i'm skipping steps here - sorry)

ok: here yah go! - the only problem with this model is that the relay on the backup battery will be on at all times, even when the alarm is disarmed, car is off, etc.

http://roshfe.com/pulsarnx/scripts/xfer/Docs/Teh_Rox0rz_Carz0rz/it_works.JPG

very confusing diagram, but i don't feel like taking the time to make it good

I think i get most of it.

Why does it say additional realys at the bottom left?

You say it that one realy will always be using power, just how much?  Wil it be draining my backup batt or my car batt?  It is very minamal to the point that i shouldnt care?

sorry dude, it's supposed to say "additional SIRENS"

and accually that diagram would work. they would NOT be on constantly (it's true ;) )

since the 86 pin is connected to the (+) for the siren, it will only flip when the alarm sends power to that factory siren.  I have seen complete alarms (cheap ones) built into the siren (brain and all) in which case it has constant power going to it at all times, but with a factory alarm system, that (+)12v on the siren is only hot when the siren is wailing.

mmmmm. big long complicated sentence to say one simple thing. I like it :-)

**additional note**

the relay for the backup battery is being used as a NC rrelay (87a and 30) so, as long as there is constant 12 volt power powering that relay, no connection is being made, and the sirens will be silent. 

As soon as that 12v supply is disconnected (i.e. battery removed), that relay will snap shut, completing the circuit, and activating the backup battery.

(The additional diodes are used to protect the 9v from a 12 surge that could destroy the battery since relays need time to flip over once power is reconnected and such)

and like I said, ignore those first two diagrams. I'll be deleting them off the servery anywhoo. they are useless :)

happy wiring!