Making an alert audible is useful for many people, but it does not guarantee that every person will notice it. Attention is finite. A demanding visual task can compete with a sound even when hearing itself is unaffected.
Availability and attention are different
An alert can exist in more than one channel and still fail at the moment it matters. The question is whether people notice the warning, understand it and have enough time to respond while carrying out the surrounding task.
Test in context
Do not assess the sound in isolation. Ask participants to perform the real journey, then observe whether they notice and interpret the alert. Pay attention to high-pressure steps, competing information and repeated warnings that may lose meaning.
Support recovery
Keep critical information available after the initial alert and offer a clear recovery route. A missed moment should not automatically become an irreversible error.