Microsoft.Win32.SystemEvents.SessionSwitch += new Microsoft.Win32.SessionSwitchEventHandler(SystemEvents_SessionSwitch); private void SystemEvents_SessionSwitch(object sender, Microsoft.Win32.SessionSwitchEventArgs e) { if (e.Reason == Microsoft.Win32.SessionSwitchReason.SessionLock) { DoSomething(); } else if (e.Reason == Microsoft.Win32.SessionSwitchReason.SessionUnlock) { DoSomethingElse(); } }