Here is a quick video of my Sentry F-2 sounding a couple of cycles of attack. This siren is very virtually brand new and will be going up for sale soon.
This siren sounds WAY better than a Model A, and the chopper is much larger too. It will nearly flip over from the startup torque if not anchored down.
http://www.youtube.com/watch?v=l8ZGXtFujM0