Option Explicit
 
Private Sub Form_Load()
    Call Hook(Me.hWnd)
    Me.AutoRedraw = True
End Sub
 
Private Sub Form_Unload(Cancel As Integer)
    Call Unhook(Me.hWnd)
End Sub

Option Explicit
 
Private Declare Function WTSRegisterSessionNotification Lib "Wtsapi32.dll" _
    (ByVal hWnd As Long, ByVal dwFlags As Long) _
    As Boolean
Private Declare Function WTSUnRegisterSessionNotification Lib "Wtsapi32.dll" _
    (ByVal hWnd As Long) _
    As Boolean
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" _
    (ByVal hWnd As Long, ByVal nIndex As Long) _
    As Long
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" _
    (ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) _
    As Long
Private Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" _
    (ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal uMsg As Long, ByVal _
    wParam As Long, ByVal lParam As Long) _
    As Long
 
Private Const NOTIFY_FOR_THIS_SESSION As Long = 0
 
Private Const WM_WTSSESSION_CHANGE As Long = &H2B1
Private Const WTS_SESSION_LOCK As Long = 7
Private Const WTS_SESSION_UNLOCK As Long = 8
 
Public defWindowProc As Long
Private Const GWL_WNDPROC As Long = (-4)
 
Public Sub Unhook(fhwnd As Long)
    Call WTSUnRegisterSessionNotification(fhwnd)
    If defWindowProc Then
        Call SetWindowLong(fhwnd, GWL_WNDPROC, defWindowProc)
        defWindowProc = 0
    End If
End Sub
 
Public Sub Hook(fhwnd As Long)
    defWindowProc = SetWindowLong(fhwnd, GWL_WNDPROC, AddressOf WindowProc)
    Call WTSRegisterSessionNotification(fhwnd, NOTIFY_FOR_THIS_SESSION)
End Sub
 
Public Function WindowProc(ByVal hWnd As Long, ByVal uMsg As Long, ByVal wParam _
  As Long, ByVal lParam As Long) As Long
    Select Case uMsg
        Case WM_WTSSESSION_CHANGE
            Select Case wParam
                Case WTS_SESSION_LOCK
                    Form1.Print Time & " - session has been locked."
                Case WTS_SESSION_UNLOCK
                    Form1.Print Time & " - session has been unlocked."
            End Select
    End Select
    WindowProc = CallWindowProc(defWindowProc, hWnd, uMsg, wParam, lParam)
End Function

mfg
brave@heart

...bis zur unendlichkeit und noch viel weiter...