An alarm that appears on screen with nothing coming out of the speaker narrows things down a long way: it was scheduled, it fired, and only the sound failed. That is a short list of causes.
This is the fork that decides everything else, and it is easy to check.
It matters because a notification is silenced by a whole set of things a real alarm ignores: the Ring/Silent switch, the notification volume, any Focus, and Scheduled Summary. Until iOS 26 no third-party app could schedule a real alarm at all, so an alarm app written before AlarmKit is sending you notifications — and “going off but no sound” is the normal behavior of a notification on a silenced device, not a bug.
If what you saw was a banner, fix it at the source: take the app out of every Focus’s block list and out of Scheduled Summary, allow its sounds, and take the Ring/Silent switch off silent. Or move to something that schedules a real alarm.
Alarms play at the ringer volume, which is a separate slider from media. Open Settings › Sounds & Haptics (Settings › Sounds on iPad) and drag the Ringtone and Alerts slider: iOS plays a sample at the exact level your alarm will use. If that sample is silent, so was your alarm.
In that same screen. With it on, the volume buttons change the ringer whenever nothing is playing, so the level can be pushed to zero at any point in the day without you noticing. Full explanation here.
On a Face ID iPhone, iOS lowers the volume of some alerts when the front camera sees you looking at the screen. It does not take the alarm to zero, but on a phone across the room quieter and silent are the same outcome — and if you woke enough to look at it, you have already triggered it. Settings › Face ID & Passcode › Attention Aware Features.
With the ringer at zero, vibration is the entire alarm. Accessibility › Touch › Vibration switches off every vibration on the device, an alarm’s included, and no app can read that switch or override it. A device on silent with that switch off produces a completely mute alarm that still looks perfectly normal on screen.
There is a known iOS 26 bug worth knowing about here, because it produces exactly this symptom. Swiping an alarm away while the device is unlocked can leave an empty Live Activity stuck in the Dynamic Island. It looks like an alarm in progress, it makes no sound, and it survives force-quitting and even deleting the app that created it. Restarting the device clears it. It affects Apple’s own sample code, so it is not specific to any one alarm app — and if what you are looking at is a stuck bubble rather than a ringing alarm, there is nothing wrong with tomorrow’s alarm.
| Suspect | Reality |
|---|---|
| Silent mode | A system alarm sounds through the Ring–Silent switch. |
| Sleep Focus, Do Not Disturb, any Focus | Alarms break through all of them. |
| Media volume at zero | Different slider. It does not set the alarm level. |
| Force-quitting the app | iOS holds the alarm, not the app. |
| A restart | Alarms survive a reboot; iOS re-arms them. |
| Low Power Mode | Does not suppress or quiet alarms. |
Every item above can be settled in two minutes with a real alarm set for two minutes ahead, from where the device actually sleeps — here is how to run that test properly. If the cause turns out to be one of the ones nobody can control, a second alarm a few minutes later is the only real answer.