Sadly (as usual) that piece of shit browser named Internet Explorer, wont trigger it.
Soon enough (on private sites) i'll have to start adding a browser check at the start of every page using the following pseudo code:
if browser is IE
display "Sorry but your browser is broken, get firefox! (link: www.getfirefox.com)"
else
display page
For now, the quick workaround is to use the click method on the input, like so:
$("input._alerts").click(function(){alert("chk was clicked");});