Top tip: this page works well when combined with a URL obfuscator such as tinyurl or snipurl.
The klaxon comes from a fabulous British quiz called QI, in which comedians explore things which are Quite Interesting. If you don't already know this, you should buy their DVD box sets post-haste. It's very funny, and also interesting.
Someone has recorded the klaxon sound and uploaded it to the intertubes. So I quickly made a webpage to unfaithfully reproduce one of their most recognisible devices. I'm hoping the BBC don't mind...
You can contact the author, who is called Alex, by emailing his name @ glastonbridge. He thinks he has fixed all the known bugs.