Updated
You set the alarm. You saw it turn on. And some mornings there is still no sound.
If that keeps happening, you are not careless and you are not a hopeless sleeper. Most of the time the alarm did not fail because it was too quiet. It failed because a setting on your phone kept it from making a sound at all, and none of those settings are visible the night before. The alarm just looks set.
This is the short version of every cause we have found, with a link to the full fix for each one. Run through it once tonight and you will know before you close your eyes.
The ringer volume is separate from the media volume
On iPhone, the ringer and alert volume is not the same slider as the media volume. You can be playing music at full blast and still have the alarm set to a level you will never hear. Open Settings, then Sounds and Haptics, and nudge the Ringtone and Alerts slider up so it is not sitting at the bottom.
A Focus or Do Not Disturb schedule is muting it
A Sleep or Work Focus that you set once can run on a schedule you have long forgotten. Alarms are meant to break through, but a misconfigured Focus, or a third party alarm app that is not allowed to bypass it, can end up silenced. It is worth reading what is actually scheduled for tonight.
Read the full fix: Does Do Not Disturb silence your alarm
The sound is playing somewhere else
This one is sneaky. If your AirPods or a Bluetooth speaker are connected, the alarm can play there instead of on the phone speaker. AirPods on the nightstand, phone across the room, and the alarm rings into an empty earbud.
Read the full fix: Why your alarm plays through AirPods
On Android, the manufacturer is often the cause
Samsung, Xiaomi, and others add their own battery management on top of Android. After a system update or a reboot, those settings can quietly stop an alarm app from running overnight. If your alarm broke right after an update, this is the usual suspect.
Read the full fix: Why your Android alarm stops working
Low Power Mode is throttling things overnight
Low Power Mode rarely kills a standard alarm on its own. Combined with an app that relies on background scheduling, it adds risk. If you are cutting it close, turn it off before bed.
The alarm is set for the wrong day
This sounds obvious and it is still the most common one. A one off alarm set for today, or repeat days that do not include tomorrow, will sit there looking on and never fire. Double check the day, not just the time.
The frustrating part is that none of this shows the night before
Every cause above is invisible when you go to sleep. The alarm says on. It looks fine. You cannot tell that the ringer is down, or that Focus will mute it, or that the sound will route to headphones, until the moment it fails at 9:03.
That gap is the reason we built Snora. Snora is an alarm you set like any other, with one difference: before you sleep, it checks itself. It reads the permissions and settings it can see on your phone, then shows one status for whether tomorrow's alarm is set up to go off: Safe, Caution, or Risk. It is a status, not a score to chase, and it is not a promise about your morning. Just an honest read on whether it will ring, so a muted alarm looks like a problem tonight instead of your fault tomorrow. The alarm and the check are free, and no account is needed.
Whatever alarm you rely on, the routine is the same. Check the ringer volume, read your Focus schedule, disconnect your headphones, and make sure the day is right. Do it once tonight, and before you close your eyes you will know whether your alarm is set up to go off.
FAQ
Why do I keep sleeping through my alarm?
Most often the alarm never actually made a sound, so there was nothing to sleep through. A setting on your phone can keep it silent with no sign the night before, whether that is a lowered ringer, a forgotten Focus schedule, or the sound routing to headphones. The fastest place to start is confirming the alarm can play out loud on the phone speaker at a level you would hear.
Can Do Not Disturb silence my alarm?
Usually not, because the built in clock alarm is designed to ring even while Do Not Disturb is on. The trouble comes from a Focus you set once and forgot, or a third party alarm app that has not been allowed to bypass it, either of which can end up muted. On iPhone you can review what is active under Settings, then Focus.
Why is my phone alarm not making any sound?
The most common reason is that the ringer and alert volume is turned down, which on iPhone is a separate control from the media volume. Raise it under Settings, then Sounds and Haptics, so the Ringtone and Alerts slider is not near the bottom. If earbuds or a Bluetooth speaker are still paired, disconnect them so the sound plays on the phone instead of an empty earbud.
Why did my alarm stop working on Android after an update?
On Android, a system update or reboot often switches the manufacturer's battery management back on, which can stop an alarm app from running overnight. Open your battery settings and allow the alarm app to run without restriction, then confirm it still has permission to schedule exact alarms. Snora reads the exact alarm and battery optimization permissions it is granted and flags them before you sleep, so you can fix them the same night.