In most places in the US it is illegal to have a siren in a residential area which is more than about 110 dB. You can have a smoke alarm that meets the national code and presents in the officially approved pattern, and I think that Those can go to 115, but only in brief bursts .
But in many places you will get a major fine for disturbing the peace if you have a very loud siren and your neighbors complain.
Which makes it difficult even to test. so that’s why there aren’t more of them sold. The manufacturers don’t want you to get mad at them when you have to pay a $1500 fine.
I believe the fortrezz is the loudest standard zwave residential siren you can get at just over 110 DB. I do think that’s louder than the aeon, but it’s still not super loud.
The alternative is to trigger a sound file on a regular speaker device that can go louder. Or find a commercial siren that runs on power and just plug it into a smart switch. Again, if you have close neighbors this may result in Municipal complaints, so just take that into account. Also, you probably have to have a license to operate a commercial siren so that’s a separate fine.
Most communities take noise complaints quite seriously.