You need to confirm this but I think if you have the intrusion/motion sensors (you should have the 4 sensor holes in your overhead console) you should have the perimeter plus sensor already installed by the factory.
My understanding is that I have intrusion - which picks up a stray moth that decides to fly around at 3AM, and the pitch/yaw sensor that picks up being towed (or in my case will go off when taking a vehicle ferry with imperceptible pitch/yaw). But I don't have a shock sensor as it is the additional module, as discussed.
I haven't found a way to turn off the intrusion and have it last past one cycle. I tried to turn it off through the instrument settings, but it only turns it off when the truck is off once, but it doesn't disable it. When camping I get the odd bug in the truck and don't want it to set off the alarm in the night. So it is no locking or it requires remembering to set perimeter only.
My question is that if I add the shock sensor, does it toggle on and off with intrusion or perimeter. I suspect intrusion (the 4 sensors in the roof), but I wanted to make sure. If I park somewhere with big trucks etc., didn't want it to go off - want to be able to set to perimeter only.