Log Gnome login/logout and lock screen events

.config_autostart_lockScreen.sh.desktop

[Desktop Entry]
Type=Application
Exec=./lockScreen.sh lock_screen.log
Hidden=false
NoDisplay=false
X-GNOME-Autostart-enabled=true
Name[en]=Log lock screen events
Name=Log lock screen events
Comment[en]=
Comment=

lockScreen.sh

#!/bin/bash

outputFile=${1:-/dev/stdout};
dateFormat=${2:-[%F %T]};

exitReport() {
    echo "$(date +"$dateFormat") Monitoring Terminated." >> $outputFile;
    exit;
}

trap "exitReport" 0;

addDate() {
    found=0;
    locked=0;

    while IFS= read -r line; do
        # If the line ends with ActiveChanged, next line is true/false.
        if [[ $line == *'ActiveChanged' ]]; then
            found=1
            continue;
        fi;

        if [[ $found == 1 ]]; then
            if [[ $line == *'true' ]]; then
                if [[ $locked == 0 ]]; then
                    echo "$(date +"$dateFormat") Screen Locked";
                fi;

                locked=1;
            else
                if [[ $locked == 1 ]]; then
                    echo "$(date +"$dateFormat") Screen Unlocked";
                fi;

                locked=0;
            fi;
        fi;

        found=0;
    done;
}

echo "$(date +"$dateFormat") Monitoring Started." >> $outputFile;

dbus-monitor --session "type='signal',interface='org.gnome.ScreenSaver'" | addDate >> $outputFile &

wait;

echo "$(date +"$dateFormat") Script Ended." >> $outputFile;

The actual filename for the .desktop file should be .config/autostart/lockScreen.sh.desktop.