i've made an external siren that works ok, before reading please be aware that the design is just thrown together and could be much more appealing to the eye if i was an engineer. I used mostly store bought parts that i destroyed to build it, but of course i'm not an engineer so i just used stuff readily available. I hope people will use this idea and tweak as needed and repost to help make the finished product look more appealling. What i did was break apart a dusk to dawn sensor from homedepot ( the kind with three wires that can be put on pretty much any light). after breaking it apart and removeing the epoxy to expose the relay i remove it and install a 12v dpdt relay just attaching the coil wires to the board. the siren is 12v, and 9-12v transformer ( mine salvage from cordless phone i think) wire transformer to siren cutting one of the leads and putting the cut ends on the relay in the normal closed position. applying power to transformer at this point will sound the siren. next is to enclose the light sensor in a (project box, gang box,ect..) something with lid, to create darkness. now power up the sensor board which is 120vac, and plug in the transformer. when dark is sensed the relay energizes and shuts off the siren. now a lamp module with a bulb attached, and a hole in the project box for light to pass. stick light sorce next to hole. When security trips, the flashing lamp causes the sensor to release the relay and sound the siren. Also the sensor board has a capacitor on it that just so happens causes a slight delay, so when the light is flashing, the siren stays on steady. also when alarm is disarmed the lights stay on, as does the siren.
