I will try to post a picture of my siren. It is basically a very small siren in a piece of PVC tube. It about 1/4" wide by 4" long tube. It has a servo plug on the end. It monitors a valid signal from the receiver. If I signal pulse is detected, the siren goes off. Once the pulse width is valid, it shuts off the siren. Very simple and these are commercially available.
Originally Posted by jglover
I got the Siren at Radio Shack. They're in the pullout drawers they have set up with all the connectors and stuff. Its operating voltage is 7-14V and its 108 Decibles. Its loud. The smaller ones arent loud at all, more like a buzzing niose, but this one will blow your ears out.
Put the 1/3 Camera in there for size comparrison