Here’s what AudioLemon has to say about it:
A Square wave controlled by 2 independent LFO’s (a rectified sine and a pulse) both with retriggered phase, and a chopper section. There are 20 MIDI CC accessible internal presets and new ones can be saved as a seperate instance or with your track.
It was designed to be used Live so it is very simple, very user friendly and sounds just about right I think. For more information just open it up and have a look inside.
You can download the free dub siren at the MaxForLive site.