Today was the annual test of the system around the Susquehanna Steam Electric Station near Berwick, PA. This T-121 is one of the outermost sirens, located in Mifflinville, PA at the fire station.
Susquehanna Nuclear tests on the 3rd Thursday of August at 11 AM, and I believe this particular siren also sounds for fire calls.
Enjoy!
https://www.youtube.com/watch?v=fGqkbiAmKg8