As others have said, this does not solve the problem that was originally posted (which I have as well). This seems to be a bug. Maybe one that comes and goes with iOS versions? Yes, I have had this multiple times as well. Again, randomly. When it's happened to me, I've noticed that NO sounds appear to work (e.g. the 'click' sound it makes when locking, the keyboard sounds, etc.). Yes, the phone is NOT on silent. No, the phone is NOT connected to any headphones, speakers, bluetooth devices, etc. Yes, the sound is set on the phone to NOT be silent. The hardware silent switch is not activated. Do Not Disturb is activated (if any of that helps with debugging). Only responding to your comment because it's the first that shows up when Googling this. This appears (to me) to be related to iOS12.4.1. It never happened to me before this. I have an iPhone X if that matters. For me, restarting the phone 'fixes' the sound issue. At least for a couple of days. Same as others, the alarm IS going off (the screen shows the alarm screen with the snooze and stop buttons) but no SOUND is coming out. It's not that it's low volume. It is NO volume.