Im sitting and listening to the attack dog bark and thought a bigger attention getter,the sound of a pump shotgun being pumped!
The wav file (the sound of the shotgun being pump/loaded) can also be found here (http://www.freesound.org/samplesViewSingle.php?id=55341). Then use a motion sensor to trigger the sound to play. There are a bunch of ways to cause the wav file to play. I use [the software] Bill's Voice Commander (BVC) (http://www.davesdomainonline.com/bvc/bvc.htm). BVC will not only play the wav file it will also speak the text I give it to speak... and it listens to/for the X10 commands (like a motion sensor) so it knows when to play or speak.
You can also do a similar project using an MP3 player, motion sensor, appliance module, and computer speaker.
My backyard voice warning can be seen in my old YouTube Video here. http://www.youtube.com/suitmanIM Good luck with your project!
If necessity is the mother of invention.... Boredom might be inventions drunken barfly at closing time.