If your alarm is quieter than you set it — or quieter on some mornings than others — there are two settings that genuinely move it, and neither one tells you it did.
This is the one almost nobody knows about, and it is the better explanation for “my alarm was silent” than any of the usual suspects.
On iPhones with Face ID, iOS checks whether you are looking at the screen before it does certain things: before dimming the display, before expanding a notification on the Lock Screen, and before lowering the volume of some alerts. That last one includes your alarm. If the front camera sees your face while the alarm is ringing, iOS reads that as “I’ve got it” and turns the sound down.
The failure it produces is very specific, and it is the exact thing that happens to people who oversleep: you half-wake, you look at the phone, the alarm gets quieter, and you go back to sleep. It is quietest precisely when you needed it loudest.
No app can detect this, prevent it, or work around it. It is not something your alarm app is doing to you, and no alarm app can undo it — not the built-in Clock either. The only fix is the switch.
Settings › Face ID & Passcode → enter your passcode → Attention Aware Features.
Attention Aware Features needs the TrueDepth camera. On a Touch ID device — iPhone SE, and most iPads — there is no such setting and no Face ID & Passcode screen to find it in. If that is what you have, this is not what is lowering your alarm, and it is worth moving straight to the next section rather than hunting for a setting that does not exist.
Worth knowing before you flip it: your screen will no longer stay lit just because you are looking at it and will dim on its own schedule, and Lock Screen notification previews will no longer wait to see your face before expanding. For most people that is a fair trade for one reliable morning, but it is a trade.
Settings › Sounds & Haptics on iPhone, Settings › Sounds on iPad.
With it on, the physical volume buttons change the ringer volume whenever nothing is playing. Nothing is playing for most of your waking day, so a press in a pocket, in a bag, or in a child’s hand sets the volume your alarm will use tomorrow morning — hours before you find out.
With it off, the volume buttons only move media volume, and the ringer stays exactly where you put it. The Ringtone and Alerts slider on that same screen becomes the only thing that can change it.
Drag the Ringtone and Alerts slider and iOS plays a short sample at the exact volume your alarm will use. Do that rather than trusting a number, because no app can tell you your alarm volume. iOS exposes no public way to read the ringer volume, to set it, or to be notified when it changes. The one volume an app can read is the media volume, which is a different thing entirely. So an app that displays “your alarm volume” is either showing you the media volume under a wrong label, or inventing the number.
Two more things are worth checking, because they change what “loud” means rather than the volume number itself.
Once the settings are right, test it from where your head actually is — and do not look at the screen while it rings, for the reason at the top of this page.