I just acquired a 2005 XJ8L. Two times, when I have locked the car with the key on the drivers door, the alarm has gone off between 15 and 30 minutes on. All by itself, with no tampering to the car.

Does anyone have this issue? Is there a fix for this? I don't have an Owners Manual to tell me if I'm locking the car incorrectly.

Thanks in advance.