Hi All - I made my own siren that hooks into the Eufy API using an Arduino mkr 1010, a bit of server-side code that you’ll need to host somewhere, and a relay. The beauty is you can hook the relay up to any siren, including (if you really wanted to) an air raid siren. Suffice to say mine isn’t using an air-raid siren; instead I’ve hooked it up to a pretty standard, but loud, siren alarm you can purchase at any hobbyist electronics store.
I’m thinking of writing up a how-to. Pop in a reply, or a heart, and if there’s sufficient interest I’ll put in the effort to write it up.