Operating The Transmitter Lock Switch
WARNING: This page is about a different car, the 2005 Mitsubishi Lancer. However, it is still accessible from the selected car via links, so may be relevant.
When the transmitter lock switch is pressed, the ETACS-ECU energizes its door lock relay to operate all the door lock actuators for 0.25 second thus causing all doors to be locked.
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.