Also noticed these errors in the Live Logging when I am trying to pair the siren:
debug Parsed 'zw device: 21, command: 5E02, payload: 01 05 00 0F 00 0F 00 ' to null
debug Couldn't zwave.parse 'zw device: 21, command: 5E02, payload: 01 05 00 0F 00 0F 00 '