The same siren as before, I've just added a protective screen and hooked up my 555 wail timer.
Since this vid I've tweaked the timer so that it cuts back on quicker during the wail. The timer assembly is shown at the end
http://www.youtube.com/watch?v=Yto68JCk4g4
Turn your speakers up for this one and listen for the echo, it's very faint. That's what you get for filming with a cell phone.
http://www.youtube.com/watch?v=K4-PMwRx8k0
Hopefully I will get a decent recording device that really captures the sound of this siren.
Any questions just ask.