You have some rather interesting finds to say the least. First off, The siren located at the Plymouth City Hall is a 12 port, Federal Model 5A, and used to be run for fire and tornado alerting. They even used it to announce the start of the July 4th parade, but I am not certain if it's even operable any longer.
The Romulus siren off Goddard Road is a Federal C-3?, 8 port, low-pitch unit. The other one at Wayne and Ecorse (Old M-17) is a 12 port high-pitch model. I believe they had one on each of the four fire stations?
The situation in Belleville is rather interesting. The siren that is on top of the police station maybe a Sterling unit. Conversely, Van Buren Twp. FD used a Sterling M-10, with a 16/16 high-pitch configuration at their old fire station #2, located on M-17 (Ecorse Road), west of Belleville Road, (Old M-56).
The abandoned Federal Model 7 that is located off Huron River Drive, and Wexford, used to be located under the old water tower that was in Belleville. When the water tower was torn down in the 1980s, the siren was moved to its present location and died after lightning struck the siren. The wires were cut to shut the siren off, and has never been repaired.
I have talked to the city council in Belleville, and they feel that a new siren system is a complete waste of money, as they have not been hit by a tornado yet. Likewise, the residents complain about the sirens being too loud for storm warnings.
Come to think of it, Sumpter Township used to have two Model 5 sirens from Federal. However, they died and went to scrap in the mid-1990s.
Huron Township still has sirens, and they often test them. I believe they are located on each of their fire stations. There would be an interesting road trip right there.