Wake-me-up audio from SW+ Alerts will not be audible if your phone is silenced, muted, on vibrate or "Do Not Disturb," however the push notifications will still be sent. This is how iOS/Android devices are set by the manufacturer -- we have no control over this. If not silenced, audio notification for the most pressing alert types will wake you up!
We are in the process of applying for the ability to override the manufacturer settings on iOS devices, which will allow the most critical alerts to sound even if your phone has audio disabled.
If severe weather is expected, especially overnight, it is best to leave your phone’s ringer or notification sounds turned on.