Ahh yes one of my favorite topics!! I (for once) actually have stuff to add to this topic..so here goes:
The Allertor in Philomont:
The Modified Allertor in Middleburg (looks awful, no wonder they took it down):
and finally this gem that has been sitting on my computer since 2002 or so, a picture of the fire chief from the Lovettsville Fire Department sitting in front of their Allertor after it was taken down:
I think Purcellville used have an Allertor as well, it was gone when I visited though... same goes for Neersville.