I would stay away from the battery backup siren, if you intentionally disconnect the main battery it will go off. This means you have to mount it in a vulnerable position so that you can use the key to shut it off. I would instead get a backup battery (DEI makes one) and maybe use two sirens. Hide them well (mines behind the fender) and loom the wiring. The battery backup continues to power the alarm after the main battery is disconnected. Don't stick the alarm brain under the driver's side dash, they'll rip it out in seconds.