The easiest would be to insert a simple php-functioncall after each insert/update query in your PHP scripts.
If you want to monitor all updates, even those made by hand etc,
you'll need to activate MySQL's logging, and check the logfiles every X seconds to see if it changed.
But remember, if you send an email for every update,then 20 updates will give 20 emails. 2k updates will give... well... email-problems.