Topic: how to make <%= observe_field return value when we uncheck the checkbx

hi i have one more Q its abt
<%= observe_field .......%>

it is doing ajax post back when i check and uncheck the check box but its passing the value when i check the check box but not when i uncheck it,is there any way we could make it work so that it always sends value,i need this as i cant use 'check_box_tag ' as i need to call a javascript code too as far as i know with 'check_box_tag' we cant call javascript and the remote function with it if we can please let me know...or please let me know how we can make observe field to return the value when the checkbox is unchecked too