I have a '99 Limited that I cannot figure out if I have a working alarm or not. I have looked under the seats and cannot find the "black box" anywhere. My keyfobs are the 3 button style with the panic button on the back. I also have the security light on the center dashboard.

The reason I think I have an alarm is that during this past winter there was one time where our front doors were frozen shut and could not open up. I was able to get it slightly open but not enough to get in. During the day the sun came up and thawed the doors and since they were open slightly, the alarm went off twice for each front door.

I have not been able to recreate that scenario even including rolling down the windows and locking the doors and reaching in to unlock the doors to set off the alarm. When the key is not in the ignition I get a slow flashing light and not the solid 30 second light that I have read about.

Could I be in some kind of valet mode where the car isn't self-arming? This is really confusing and after searching for many hours, I can't find a post with a similar problem.

You might have a factory alarm, and sounds like you do. But in my opinion, factory alarms don't do much. No impact sensor and not much of a starter disable if any. No type of alarm or security device is able to guarantee total prevention of theft, but the more you add, the harder and longer it would take to steal your baby. Also most alarms, factory or aftermarket have very few security features, it's mostly convenience. I love the convienience features, but on my car I have starter and ignition disable (normally open so still works if the battery is cut) and I added a siren inside the car so if someone is trying to violate my baby, it's not going robe pleasant.

Call a local dealership with your VIN and they should be able to tell you if you have a factory alarm or not. This is what I did on my 99 limited.