Hi @nvrpc1. The Ring Alarm is not compatible with any third-party Z-Wave sirens. We have the Dome Siren, which can be used as an additional siren and can be installed indoors. The Dome Siren is not available for the UK at this time. For our neighbors located in the UK, we have the Ring Alarm Outdoor Siren that can be installed outdoors. The Outdoor Siren is currently not available for purchase in the US or Canada.
If you have any Ring Security Cameras that have a siren, you can use the Linked Devices feature to have the sirens from your Cameras go off when the Ring Alarm is triggered. You can read more about this feature in our Community post here. I hope this helps clear things up.