Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
"DisableLockWorkstation"=dword:00000001

#include %A_ScriptDir%\lock.ahk
notify_lock_unlock()
on_lock()
{
   msgbox, locked
}

on_unlock()
{
   msgbox, unlocked
}

;Initialize global constants
WTS_SESSION_LOCK        :=    0x7
WTS_SESSION_UNLOCK        :=    0x8
NOTIFY_FOR_ALL_SESSIONS    :=    1
NOTIFY_FOR_THIS_SESSION    :=    0
WM_WTSSESSION_CHANGE    :=    0x02B1

notify_lock_unlock()
{
    Global WM_WTSSESSION_CHANGE
    Global NOTIFY_FOR_ALL_SESSION
    hw_ahk := FindWindowEx( 0, 0, "AutoHotkey", a_ScriptFullPath " - AutoHotkey v" a_AhkVersion ) 
    OnMessage( WM_WTSSESSION_CHANGE, "Handle_WTSSESSION_CHANGE" ) 
    success := DllCall( "wtsapi32.dll\WTSRegisterSessionNotification", "uint", hw_ahk, "uint", NOTIFY_FOR_ALL_SESSIONS )
    if( ErrorLevel OR ! success ) 
    {
        success := DllCall( "wtsapi32.dll\WTSUnRegisterSessionNotification", "uint", hw_ahk )
        ;If DLL registration fails, wait 20 seconds and try again
        Sleep, 20000
        notify_lock_unlock()
        ;MsgBox, [WTSRegisterSessionNotification] failed: EL = %ErrorLevel%
    }
    return
}

Handle_WTSSESSION_CHANGE( p_w, p_l, p_m, p_hw )
; p_w  = wParam   ;Session state change event
; p_l  = lParam   ;Session ID
; p_m  = Msg   ;WM_WTSSESSION_CHANGE
; p_hw = hWnd   ;Handle to Window
{
    Global WTS_SESSION_LOCK
    Global WTS_SESSION_UNLOCK
    If ( p_w = WTS_SESSION_LOCK ) 
    {
        on_lock()
    }
    Else If ( p_w = WTS_SESSION_UNLOCK ) 
    {
        on_unlock()
    }
}

FindWindowEx( p_hw_parent, p_hw_child, p_class, p_title ) 
{

    return, DllCall( "FindWindowEx", "uint", p_hw_parent, "uint", p_hw_child, "str", p_class, "str", p_title ) 
}