Stolen Cats 2nd Time, OEM Alarm Wiring, 2014 Ford F-150 XLT

So I park my 2014 F150 XLT outside my shop under a veranda since I got it in 2014. Never had any problems until last month, someone crawled under the truck and cut off both cats. Wow. That was expensive. After the dealer installed new cats for me, I got to thinking, so I crawled underneath and welded up a couple steel bars to interfere with it happening again.

I'm just dumb I guess.

Last Monday someone cut off the cross brace and cat on one side but not the other.

So, now I want to do the following: I have a microwave transducer with a warn output and an alarm output - both are switched ground outs. I figure I could mount the transducer under the truck and adjust the sensitivity to have it trip localized to the cat area only. I need to find a "ground while armed" output from the OEM alarm (that has no shock sensor.) I need this to enable the microwave transducer only while the OEM alarm is enabled in order to avoid false triggers. I could then wire the warn output to a chirp horn mounted under the truck and wire the trigger output to the door pin switch via a diode in order to trigger the OEM alarm to start honking if someone is trying to steal my cats again.

But what do I know? I just repair the electronics that control espresso machines, I'm not a car wiring guy like y'all.

Where can I get the wiring and location information to help me with this? Alternatively if anyone has a better idea how to skin this cat (no pun intended) I'd like to hear it. If I wire the ground to a relay that provides ground when the key is off only, I'm afraid the microwave warn chirp may become obnoxious. That's why I'm looking for a ground while armed output from the OEM alarm. I'm trying to do this with materials I happen to have already.

Any help would be appreciated, thanks!

Oh, and I found out why the uptick in the crime at my spot. A food bank recently opened across the street from me. That's what has caused increased traffic by my business after hours.

Well I figured this out on my own, it wasn't too difficult. I used a relay to interrupt the yellow wire from the latch at the rear passenger door. I did this at the body control module that's located in the passenger kick panel, wire I cut is on the grey 26pin connector on pin 15. The relay connection is between pins 30 and 87a which is common and normally closed. The coil of the relay is constantly hot while the engine is off - again, via another relay. When the microwave transducer senses interruption in it's bubble and sends out a ground, that ground to cause the relay coil to energize, thus opening 30 and 87a and causing the OEM alarm to believe the door has been opened and be fooled into tripping. I added the second relay for main power to be supplied to the Microwave transducer only while the key is off, because I didn't want the dome light coming on while I was driving. I ended up not using the warn output from the Microwave transducer because it wasn't long enough of an output to cause enough of a warning on the chirp siren I have.

One hiccup I ran into that you can avoid is - don't connect to the drivers door pin via the way I suggested. This particular pin causes a stupid delay to occur before triggering the OEM alarm system.