I've never seen any sirens in High Ridge. I've also never seen any sirens in unincorporated areas and towns, such as Brynes Mill, Barnhart, Imperial, House Springs and Kimmswick to name a few.
Along with a few scattered older sirens, here's the newer siren installations:
Arnold: ATI system
Pevely: Whelen WPS-2909's
Herculaneum: Whelen WPS-4004's
De Soto: Whelen WPS-4004's
Hillsboro: Whelen WPS-4004's
Festus: Whelen WPS-4004's
There's also a Whelen omnidirectional siren (2 cell) about 1 mile south of Festus on Highway 61, that looks like it belongs to a company.