Trigger code to run on page when an event of site occurs

Anney

irs not a question if copying the code. What I want to happen is that when a select is made in a combo box on the header a change event takes place that runs code in the SITE page as it is a header.

when this event happens I pass the value to the PAGE using the session Setitem and getitems and I want to run a function that queries a collection immediatey

so my question is how to trigger this function automatically?