One of the problems with alarm sound(s) is that they first need to be heard, whatever the orientation of carer to patient is, then they need to draw attention to the physical location of the alarming device (by audible and visual means, but initially audible), ideally convey a sense of urgency (perceived urgency to the carer) associated with the alarm (that's related to the situational urgency in the current clincial context i.e. the condition of the patient), so that the response to the alarm is both timely and appropriate.

Ideally this means that alarm sounds should convey some information about the physiological source of the alarm, i.e. the parameter or set of parameters that generates the alarm(s) hence the status of the patient. They should not produce clinically insignificant or "false alarms", neither should they miss clinically significant alarms or "true positives". Unfortunately setting alarm limits is still a bit hit and miss because it depends upon clinical context and the ever-changing status of the patient connected to devices. Sounds are not the only problem associated with current alarm technology.

Sounds & visual indicators allow carers to locate and respond to a clinically significant alarms that may be occurring's difficult enough for individuals with normal hearing characteristics who work in busy cinical areas with a wide range of devices.

Both visual and audible alarms are absolutely necessary - audible to draw the operators' attention to the alarm source, wherever they are, within earshot, and visually to locate the alarm(s) once attention has been drawn to them. Standardised alarms can be designed to address these needs but there's an element of "natural" response to carefuly designed alarm sounds , that convey important information, and "learned" responses to additional information conveyed in the alarms.

What I'm getting at is that it's difficult enough getting to grips with what's required for individuals with normal hearing - thus it's even more awkward designing for individuals with different hearing characteristics that are outside the norms. It must be extremely difficult to cope in a critical care area where there are lots of alarms. I guess there's more reliance on colleagues, to some extent, and the visual cues.