How to make a siren (!)

"Any old metal detector from the flea market and 3 bucks for the 9 volt it needs can get you some pretty good siren type effects pumped right through the 3/4 inch headphone jack with volume/level control.Most have a built in speaker as well. Move a metallic object around under the detector for variations. Use different types of metal to bug out further."
:submitted by the arkmaster, www.blackark.com

This is taken from Scroll III : Sound Sources and Manipulation on The Dub Scrolls. It's telling you how to make a siren.

http://www.interruptor.ch/dub_sound.shtml