Alarm Audible Alert in Multiple Client Windows

I am triggering an audible alarm when alarms become active at certain times of day. I’ve bound the trigger property of the alarmNotification tool to a boolean property called alarmActive. When alarmActive changes to “1”, the trigger fires. This works fine for one client window, but once three or four client windows are open simultaneously the audible alert only fires in one instance of the client.

Any ideas what could cause this?

Thanks for your help