KEY WARNING CHIME (WITHOUT INTELLIGENT KEY): System Description

WARNING: This page is about a different car, the 2013 Nissan Armada. However, it is still accessible from the selected car via links, so may be relevant.

With the key inserted into the key switch, and the ignition switch in the OFF or ACC position, when driver's door is opened, the warning chime will sound.

BCM detects key inserted into the ignition switch, and sends key warning signal to combination meter with CAN communication line.
When combination meter receives key warning signal, it sounds warning chime.