What is this?

[degas]

Transducer removal tool? Horn?

There's a patent number that Google can't figure out: 209356 HU.

 

[surfstud31]

They look like transducer plugs. You use them to plug the hole while taking out a transducer to clean it. But not certain.

 

[Calif. Ted]

a "Diaphragm Fog Horn" you blow in the small hole on the side. There is a diaphragm of what looks like plastic wrap across the big hole.
https://www.plastimo-pro.com/en/446810-trump-and-mini-trump

 

[Timm R Oday25]

I bought one years ago . Very simple ,very durable and very loud . Rare that something like this works without an app !

 

[rgranger]