The short answer
An iPhone alarm that does not ring is almost always one of four things: ringer volume at zero, audio routed to a Bluetooth device, an alarm saved for the wrong AM or PM, or a Focus mode. This guide works through all of them, then the less common causes.
This article is served in full from the help centre, which is where alarm troubleshooting lives so it can also deflect support load. The blog template renders the same content once the MDX pipeline is connected.
Where to read it now
See iPhone alarm not going off? Every fix, in order for the complete guide, including the four causes worth checking first and the recurring silent-alarm defect.