This circuit use only 14 components, all of easy acquisition and low price (here in Brazil at least) and can be mounted on a plate trial (which is what I did).
I will tell the story of this circuit. I made a whistle and acute with the 555 ci (which became the second block) and the following thought: if I on the other controlling the second IC 555, have a break in the whistle, thus swinging a whistle. But when you mount the circuit, realized that he played a voltage on pin 5 of IC 2 and change the swing of it! Thus the siren this project!