After some hunting, I think I've located that siren. Being that Somerset is a small town, my first guess for where the siren was located was the local fire station. I then found that there's a subdivision in that same area that looks just like the one in the video.
So, after some more hunting to figure out exactly where the fire station was (Google's address info is a bit messed up in that area), I finally found it on street view. The image isn't the best, but if you look closely, you'll see what appears to be a T-128 on a pole to the right of the station:
http://goo.gl/maps/CmEQ
(Also, for those who are wondering how to get the "goo.gl" links, once at Google Maps, click on the "New!" icon, scroll down until you find "URL Shortening", then click "Enable". Save the changes and reload the page).