Keyless Entry Horn ANSWERBACK Function
WARNING: This page is about a different car, the 2004 Mitsubishi Galant. However, it is still accessible from the selected car via links, so may be relevant.
If the keyless entry transmitter is used to send 2 lock signals to the ETACS-ECU, the first signal locks all doors, the liftgate, and the glass hatch, while the second signal sounds the horn once.