Noticing db changes that don't happen in rails?

I am working on a rails application using MySQL as the database. The customer has a legacy application which can update records in the database. I want rails to know when this happens but things like callbacks or observers will not work because the updates are not happening in rails. I need rails to know because when these records change I need to tell some web services about them. The same thing applies I think if one used a MySQL gui to change some records, the web server would not know about the changes. The only thing I can think of doing is constantly running some ruby script that checks to see if the database has changed, but I really do not want to do any type of polling. I may be completely misinformed about how some of these things work. Any help would be greatly appreciated.