Tool

Why your alarm did not go off

The alarm is on, and the morning is silent. Pick the app the alarm lives in and what exactly happened: the list keeps the causes that fit your case, with the path to the setting.

Any clock app
Do Not Disturb without an exception for alarms
A mode’s exceptions can allow or block alarms. On many phones they are allowed by default, but with the exception off the mode silences the alarm along with everything else. Google’s Clock then tells you: "Do Not Disturb silenced your alarm."
Where to look: Settings → Modes → your mode → Notification filters → "Alarms & other interruptions". On Samsung: the sounds section inside Do Not Disturb settings, with a separate slider for alarms.
Google Clock
The alarm’s sound is set to silent and vibration is off
Google’s Clock help says: "If your ringtone is set to silent and vibration is off, your alarm won't go off." The line sits in the section about the alarm’s sound, so it is about the alarm’s own ringtone. Clock warns you when an alarm’s sound is set to silent.
Where to look: Open the alarm in Clock and pick a sound for it, or turn vibration on.
Any clock app
Alarm volume is down to zero
The alarm has its own volume slider, separate from calls and media. When nothing is playing, the volume buttons change media volume, so they will not raise the alarm. Google’s Clock warns you if the alarm went off with the volume below 30%.
Where to look: Settings → Sound & vibration → alarm volume. The section is named differently from one shell to another.
Samsung Clock
Samsung silences the alarm along with system sounds
With this option on, the alarm goes quiet along with system sounds and only vibrates. Samsung suggests turning it off if your alarm only vibrates.
Where to look: Clock → More options → Settings → "Silence alarms when system sound is off".
Samsung Clock
The alarm went to your headphones
Sound Assistant has an option to play alerts through headphones, so the alarm can ring in Bluetooth earbuds sitting in their case. Samsung’s troubleshooting says to turn that option off if you cannot hear the alarm.
Where to look: Sound Assistant → the option that plays alerts through headphones.
Google Clock
Two alarms less than five minutes apart
A rule from Google’s help: if two alarms are less than five minutes apart, the first one may be cancelled. Leave at least five minutes between them.
Where to look: Clock → the Alarm tab: look at the times of neighbouring alarms.
Google Clock
Battery Saver
According to Clock’s help, Battery Saver may have prevented your alarm from going off. The same page gives two fixes: turn Battery Saver off, or add Clock as an essential app in its settings.
Where to look: Settings → Battery → Battery Saver.
Google Clock
Clock notifications are turned off
According to Clock’s help, with notifications for the Clock app switched off it shows: "To hear your alarms, turn on Clock notifications in Settings."
Where to look: Phone settings, under the Clock app’s notifications.
Google Clock
A streaming track instead of a ringtone
For an alarm that plays a track from YouTube Music or Spotify, Google’s help says you need a paid subscription. Free Spotify only lets you pick a playlist and may play ads. A plain system ringtone is the safer choice.
Where to look: In Clock, open the alarm and pick a ringtone from the system sounds.
Samsung Clock
The phone restarted and is waiting for the password
With Samsung’s strong protection enabled, alarms do not work after a restart until the password is entered. If the phone updated and restarted overnight, in the morning it is waiting to be unlocked.
Where to look: If the phone asked for the password after a restart in the morning, this is the cause.
Any clock app
The phone was switched off
Samsung says it directly: Clock and its alarm do not work while the device is off. Some models from other brands, including some Xiaomi phones, have an alarm that works when the phone is off, but that is a feature of a specific model, not of Android. The safer habit is to silence the phone at night rather than switch it off.
Where to look: Check whether the phone ran out of battery overnight.
Another app
The app was not opened after a restart
All scheduled alarms are cancelled on shutdown, and the app has to set them again after the phone boots. That only works if the app has been opened at least once.
Where to look: Open the alarm app after a restart and make sure the alarm is set.
Another app
The app was stopped with Force stop
Since Android 15, force-stopping an app cancels everything it had scheduled until you open it again.
Where to look: Settings → Apps → the app: do not press Force stop, and after a stop open the app again.
Another app
The app does not set a proper alarm
Per the Android documentation, an alarm set as a proper alarm clock (the setAlarmClock method) fires even when the phone is in deep sleep: the system leaves Doze shortly before it. Ordinary exact reminders can be delayed in that mode.
Where to look: Test the app for real: the method is described below.

How to test an alarm in a minute

Set an alarm one minute ahead, lock the phone and wait. Xiaomi’s help suggests the same. Sound and volume show up straight away.

Overnight causes will not show this way: Battery Saver, a restart after an update and deep sleep only appear after a long idle stretch.

The reminder came, but late

That is no longer about the alarm. It is about exact reminders and the battery limits of manufacturer shells. The checking order for your brand is in a separate tool.

Notification settings checker

The article: eight causes with quotes from the help pages