They work, but in my experience, not as well as they used to. Alot more people are using the technique these days. I believe some of the dogs have kinda gotten wary of it.? Just an opinion, I can't prove that of course. However, I have noticed less and less response to a siren over the last 15 years, and it's happened gradually. I've seen this in all areas that I've hunted, not just the areas that I frequently hunt.
Len, I used to have one mounted in my pickup. An electronic one with multiple sound boards.......extremely loud. Got if from a fire truck manufacturer. Controls were in the cab, horn was under the hood.
I then tried a couple of the handheld ones after I wrecked that truck in 2000. You can download the sounds into the foxpro (at least the old foxpro), I have two different siren tones downloaded into mine. Unfortunately, I don't recall where I downloaded them from. I probably searched google until I found one. It's been about 8 years since I did that, so my memory isn't so good.