Screamers are 100db+. To get that you have to drive a piezo at about 100V near it's maximum resonance point and engineer the case to create a resonant cavity.

To generate that voltage, you're likely going to need an autotransformer. And nobody stocks these off the shelf--they're a custom order magnetics part. (If you find a better circuit topology or a place that stocks the appropriate autotransformer, do please let me know.)

Of course, if you just want a wimpy beep, there's lots of options. :) But if you want something offensively loud, you're going to find that there is more engineering here than you think.

It's a good project, but it isn't "easy".

http://www.picbasic.co.uk/forum/showthread.php?t=16855 http://www.instructables.com/id/How-to-make-an-Arduino-drive...