You may use the following event-functions of the 'ThisWorkbook' module
Private Sub Workbook_SheetActivate(ByVal Sh As Object
'manage your checkbox as you wan
'Sh is the new active worksheet
End Sub
Private Sub Workbook_SheetDeactivate(ByVal Sh As Object
'manage your checkbox as you wan
'Sh is the new active worksheet
End Su

or the event-functions of the worksheet module
Private Sub Worksheet_Activate(
'manage your checkbox as you wan
End Su
Private Sub Worksheet_Deactivate(
'manage your checkbox as you wan
End Su