You can just add a DEI 509U ultrasonic sensor to your existing alarm. The glass break sensor is a bit redundant in my opinion because as soon as you break the glass, the ultrasonic sensor will trigger. In my opinion, a better deterrent is a microwave field sensor with a warn away function. It totally kills a thief's confidence and sends them the message that this car is different when it starts beeping before they even touch it. I'm hooking a relay between my microwave sensor and dash cam so that it starts recording as soon as the warn away is triggered. That's all uploaded to the house via wifi too so I can just check what's going on out there from my PC.Alarm worked.
Last Wednesday someone tried again. Alarm woke me up and I got out there before they got anything, but not before they did $3500 worth of damage to the door, the window, the dash, and the Pioneer head unit trying to pry it out of the dash. (State Farm has been awesome though, they're even shipping me a better head unit than I had because Pioneer discontinued the one I was using.) They had to resort to shattering the window because Jimmi Jammers (which I installed after the previous attempt) kept them from just knocking in the lock cylinder and opening the door like they did last time.
They had my CB radio and my Ryobi One+ car charger and batteries out of my console and on the front seat, but they left them and ran off when I turned on the porch light.
I think I'm going to upgrade to an alarm that has a glass break sensor and adjust the sensitivity up some more.