This is a 2 horsepower Decot Engineering Works siren. It is smaller than the 3 horsepower (Monessan, PA) and 5 horsepower (Seattle, WA). The one brochure I've seen from this company goes back and forth calling it a 'Two Tone Siren' and simply a 'Decot Siren'. It is most likely 10-15 ports which was the standard sound for most of their sirens. Would have been built at their small factory in St. Paul, Minn. anywhere between 1943 to about 1950.
The shroud looks original and uses the top panel from what was also used for the 5 horsepower model's shroud top. Some of these sirens had a more proportionate top (
Wessington Springs, SD had one like this in years past). Their shrouds were never fine art.
Decot Engineering Works was a small company orchestrated by John McGrath and Robert Fullerton. They meant well but just really didn't know how to successfully mass-produce and mass-market these sirens which was one of the reasons that led to their premature downfall. Sirens from Decot Engineering Works are very uncommon... here's the former factory site area:
https://goo.gl/maps/pJPfmsakpSm