Hello
You can write a program to monitor the file's last modification.
System.IO.FileSystemWatcher can be the ideal class to work with.
For example
string filePath = @"[directory of your excel file]";
FileSystemWatcher watcher = new FileSystemWatcher();
watcher.Path = filePath;
watcher.NotifyFilter = NotifyFilters.LastWrite;
watcher.Filter = "[name of your excel file ex. myexcel.xls]";
watcher.Changed += new FileSystemEventHandler(OnChanged);
watcher.EnableRaisingEvents = true;
Hope this will help you.