One solution is a script which runs when logging into the desktop, and which catches dbus messages. After resume from suspend the screen is locked, and after entering the password, there is an Unlock event on dbus.

(Thanks to Kim SJ for putting me on the right track. I have no ScreenSaver signals, but found another interface to use).

In ~/.config/autostart/, I have a .desktop file which starts a bash script:

$ cat ~/.config/autostart/mymonitor.desktop

[Desktop Entry]

Categories=System;Monitor;

Comment=Monitor dbus for unlock signals

Exec=/usr/local/bin/unlock_monitor

Name=unlock_monitor

Type=Application

The unlock_monitor monitor script reads dbus messages from com.canonical.Unity.Session and does stuff on Unlocked signals:

#!/bin/bash



dbus-monitor --session "type=signal,interface=com.canonical.Unity.Session" --profile 

| while read dbusmsg; do

    if [[ "$dbusmsg" =~ Unlocked$ || "$dbusmsg" =~ NameAcquired$ ]] ; then

        sleep 5

        notify-send "$(basename $0)" "Unlocked or freshly logged in..."

        # ...

    fi

done

When logging in, there is no "Unlocked" signal, but there is a "NameAcquired" signal when dbus-monitor starts.