It might be difficult to add factory keyless entry. Maybe someone else here can chime in, but it's my understanding that there are 2 BCMs. The Regular BCM and the Premium BCM (Body Control Module). This is the computer that controls many things about the Libby - the lighting, interface to the overhead trip computer, Sentry key stuff, Alarm stuff, etc. You'd want to try to determine which you have first. I think Cruise control is one of the other features that would require a premium BCM.
My guess is that if you determine that you dont have a premium BCM, you'll do better to do an aftermarket alarm.
I do have to say tho, that I really do like the alarm system in this vehicle. It's pretty simple - when you click the clicker or lock the doors using the power lock, it activates the alarm. The Jeep won't start unless you have a specially chipped key, so my old (non-chipped) keys will start the Jeep, but it dies after like 5 seconds. So even if someone did hotwire it, they wouldn't be able to get far.
Here's a tidbit from the EVIC/OTIS (Mini Trip Computer) installation that might help you determine which BCM you have:
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The only KJ's that you can add an OTIS/EVIC to must have the Premium BCM installed on it.
You have a Premium BCM if you have any one or more of the following options:
Keyless Entry
Steering wheel mounted radio controls
Fog Lights
If you do not have any of the above options, there is a good chance the you have the "Base BCM" and you cannot add an overhead console. However, you can check with your dealer to scan your BCM to see which one it is. (You may even be able to replace your base BCM with a premium BCM to your KJ, though I do not know.)
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Once you've figured out what you've got, post back and we'll stir the pot a lil!
-Blu