Every PC & NC Work Station that I have worked on has had some kind of volume control where the end user can set the volume levels to their personal tastes & every messaging service I have ever worked with came with some kind of standard
"Ding ...You just got a message"
But if user has volume turned down, they will not hear that.
On the AS/400 the standard messages come with two additional features, which I call "Priority" and "Extremely Rude."
The first "Priority" deal puts the message at the top of the user Message Queue & makes it a required reply ... the user cannot delete it from their Queue ... they have to do some kind of "Yes I see that" reply & this is time stamped, so the receiver of the confirmation sees the time the confirmation was given.
The second "Extremely Rude" basically goes out coded "I do not care what the end user is doing right now ... INTERRUPT THEIR SCREEN with my message."
Extremely Rude can be combined with Priority, so that user cannot just click ignore - I will read this message later - they have to respond to it.