Key-In-Ignition Warning Chime
WARNING: This page is about a different car, the 2004 Mercury Monterey and 2004 Ford Freestar. However, it is still accessible from the selected car via links, so may be relevant.
When the key-in-ignition switch closes, it grounds an input to the instrument cluster, which then sounds a warning chime, provided that the ignition switch is off and the driver door is open. The instrument cluster will sound a steady tone, which will continue until the key is removed, the ignition switch is rotated to the RUN position, or the driver door is closed.