How can I lock an application after period of user inactivity?

My post on StackOverFlow.com

I have a fat Windows application written in VB6. User must log into the application to use it. I need to log the user out after a period of inactivity. There are over 100 separate forms with one Main form that is always open after the user logs in, so I am looking for an application solution not a form level solution.

Here is the solution I decided upon. I wanted to document it properly. As this is the approach I had envisioned, it is not my code. Someone smarter than I did awhile ago.
I simply implemented the solution into my application.

The app is an multiple-document interface app.

Private Declare Function UnhookWindowsHookEx Lib "user32" (ByVal hHook As Long) As Long
Private Declare Function CallNextHookEx Lib "user32" (ByVal hHook As Long, ByVal nCode As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (pDest As Any, pSource As Any, ByVal cb As Long)
Private Declare Function GetAsyncKeyState Lib "user32" (ByVal vKey As Long) As Integer

Private m_hDllKbdHook As Long

Private Type POINTAPI
x As Long
y As Long
End Type
Private Declare Function GetCursorPos Lib "user32.dll" (ByRef lpPoint As POINTAPI) As Long


Global variables to hold DateTime last user activity and if mouse and keyboard activity has occurred

Public KeysHaveBeenPressed As Boolean
Public HasMouseMoved As Boolean
Public gLastUserActivity As Date

Code to detect keyboard activity

Public Function HookKeyboard() As Long
On Error GoTo ErrorHookKeyboard
m_hDllKbdHook = SetWindowsHookEx(WH_KEYBOARD_LL, AddressOf LowLevelKeyboardProc, App.hInstance, 0&)
HookKeyboard = m_hDllKbdHook
Exit Function
ErrorHookKeyboard:
MsgBox Err & ":Error in call to HookKeyboard()." _
& vbCrLf & vbCrLf & "Error Description: " & Err.Description, vbCritical, "Warning"
Exit Function
End Function
Public Sub UnHookKeyboard()
On Error GoTo ErrorUnHookKeyboard
UnhookWindowsHookEx (m_hDllKbdHook)
Exit Sub
ErrorUnHookKeyboard:
MsgBox Err & ":Error in call to UnHookKeyboard()." _
& vbCrLf & vbCrLf & "Error Description: " & Err.Description, vbCritical, "Warning"
Exit Sub
End Sub
Public Function LowLevelKeyboardProc(ByVal nCode As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Static kbdllhs As KBDLLHOOKSTRUCT
If nCode = HC_ACTION Then
'keys have been pressed
KeysHaveBeenPressed = True
End If
LowLevelKeyboardProc = CallNextHookEx(m_hDllKbdHook, nCode, wParam, lParam)
End Function

Code to detect mouse movement:

Public Sub CheckMouse()
On Error GoTo ErrCheckMouse
Dim p As POINTAPI
GetCursorPos p
If p.x <> LastMouse.x Or p.y <> LastMouse.y Then
HasMouseMoved = True
LastMouse.x = p.x
LastMouse.y = p.y
End If
Exit Sub
ErrCheckMouse:
MsgBox Err.Number & ": Error in CheckMouse(). Error Description: " & Err.Description, vbCritical, "Error"
Exit Sub
End Sub



On the Main parent Form:
Added a timer:

Private Sub muTimer_Timer()
CheckMouse
'Debug.Print "MU Timer Fire"
'Debug.Print "Keyboard:" & KeysHaveBeenPressed & " - " & "Mouse:" & HasMouseMoved
If HasMouseMoved = False And KeysHaveBeenPressed = False Then
If DateDiff("m", gLastUserActivity, Now) > gnMUTimeOut Then
muTimer.Interval = 0

Else
'Debug.Print " dT "; DateDiff("s", gLastUserActivity, Now)
End If
Else
HasMouseMoved = False
KeysHaveBeenPressed = False
gLastUserActivity = Now
End If
'Debug.Print " dT "; DateDiff("s", gLastUserActivity, Now)
End Sub

Also on the MainForm load event:

Private Sub MDIForm_Load()
HookKeyboard
end sub

Private Sub MDIForm_QueryUnload(Cancel As Integer, UnloadMode As Integer)
UnHookKeyboard
end sub