’03 F150, APS-996a

I’m still in the process of installing an Audiovox APS-996a in my truck (off and on for a month now)…

I just found out that the backup battery I purchased for it (a DEI – I don’t remember the model number), will not work with this unit.  Does anyone know of one that will?

Also, I have a question regarding routing the cables through the grommet in the firewall.  It’s an ’03 F150 automatic and there’s an existing hole there for the manual transmission option.

My question is – what’s to stop someone from just popping the driver’s side window, immediately reaching in and cutting every cable routed through that hole?

I’m pulling power for the alarm from the ignition harness, so my  alarm will still be powered, but if they cut the wire going to the siren (and it goes silent), what good does that really do?  I would imagine that someone has an effective cure for this.

I’ve already looked for a more suitable place to drill another hole to no avail.  Locking the hood, hiding the siren, etc. doesn’t seem to be of much use if someone can just cut the wire going through this hole.

Finally, how would I tie in 1 (or maybe two) piezo’s into this setup?

Thanks in advance!!

It does have the option of using the factory horn in conjuction with the included siren.  Are you recommending that I use this in addition to, or in replace of the included siren?

I'd use both as long as it says you can.