Public Class Form1
    Dim WithEvents T As New Timer With {.Interval = 3000, .Enabled = True}
    Declare Auto Function SendMessage Lib "user32" (hWnd As IntPtr, wMsg As _
      Int32, wParam As Int32, lParam As Int32) As Int32
    Declare Auto Function SystemParametersInfo Lib "user32" (uAction As Int32, _
    uParam As Int32, ByRef lpvParam As Boolean, fuWinIni As Int32) As Boolean
    Const WM_SYSCOMMAND As Int32 = &H112
    Const SC_SCREENSAVE As Int32 = &HF140
    Const SPI_GETSCREENSAVERRUNNING = &H72
 
    Private Sub T_Tick(sender As Object, e As System.EventArgs) Handles T.Tick
        Dim IsRunning As Boolean
        SystemParametersInfo(SPI_GETSCREENSAVERRUNNING, 0, IsRunning, 0)
        If IsRunning Then
            SendKeys.Send("{ESC}")                                  ' Aus
        Else
            SendMessage(Me.Handle, WM_SYSCOMMAND, SC_SCREENSAVE, 0) ' Ein
        End If
    End Sub
End Class