Android alarm not going off? Six settings to check tonight
If your alarm didn't ring, rang late, or rang so quietly you slept through it, the cause is almost never the app you chose. On Android it is usually the operating system deciding — quite deliberately — that your alarm was less important than your battery.
Here are the six things that cause nearly every case, in the order worth checking. The first one alone accounts for most of them.
1. Battery optimisation is killing the app overnight
This is the big one. Android aggressively suspends apps it thinks you aren't using, and an alarm app you last opened at 11pm looks exactly like an app you've abandoned. When the system suspends it, the alarm never fires.
Go to Settings → Apps → [your alarm app] → Battery and choose Unrestricted. On some phones this lives under "Battery optimisation" as a separate list — find your alarm app and set it to "Don't optimise".
If you have a Xiaomi, Samsung, OnePlus, Oppo, Vivo or Huawei phone, this step is not optional. These manufacturers add their own app-killer on top of Android's, and it is far more aggressive. Look for "Autostart", "Protected apps", "Battery manager" or "Sleeping apps" in your settings and allow your alarm app in every one of them. The site dontkillmyapp.com has per-manufacturer instructions and is worth ten minutes of your time.
2. Exact alarm permission was never granted
Since Android 12, apps need explicit permission to schedule an alarm at an exact time. Without it, Android is free to shift your alarm by minutes — or to hold it until the phone next wakes up, which might be well after you needed to be out of bed.
Check Settings → Apps → [your alarm app] → Alarms & reminders and make sure it's allowed. Many people grant every permission an app asks for except this one, because it sounds optional. It isn't.
3. Notifications are off, so the alarm has no way to reach the screen
A full-screen alarm arrives as a high-priority notification. If you denied notifications — or if the app's alarm notification channel specifically was switched off, which is easy to do by accident when you swipe a notification away and tap the wrong option — the alarm may run without ever surfacing.
Go to Settings → Apps → [your alarm app] → Notifications and confirm both the app and its alarm channel are enabled, with importance set high.
4. Volume: the alarm slider is separate from everything else
Android keeps separate volume levels for media, ringtone and alarm. Turning your phone down at night usually adjusts ringtone or media, leaving you convinced the phone is loud when the alarm channel is nearly silent.
Press a volume key, tap the settings icon that appears, and check the alarm slider on its own. A genuine alarm app plays on this channel deliberately, because it's the one that keeps working through Do Not Disturb.
What about Do Not Disturb and silent mode?
Alarms are meant to bypass both. Android's own Clock app does, and any properly built alarm app does too, because the alarm audio channel is exempt by design. If your alarm is genuinely silenced by DND, it is almost certainly playing on the media or notification channel instead — which is a sign of a poorly built app, not a phone problem.
5. The phone restarted overnight and the alarm never came back
Updates, crashes and low battery can all restart a phone at 3am. When that happens, every scheduled alarm is wiped from the system and has to be re-registered by the app on boot.
Well-built alarm apps do this automatically. There's a subtlety even good apps get wrong, though: between a restart and the first unlock, the phone's storage is still encrypted, so an app that stored its alarm times in normal storage cannot read them and re-arms nothing. If you've ever restarted a phone overnight and had the alarm silently vanish, this is probably why.
6. You dismissed it in your sleep and don't remember
This is more common than people believe, and it is not a memory problem. Waking briefly, performing a simple action and returning to sleep with no recollection is ordinary behaviour during deep sleep — the part of your brain that forms memories is still offline while the part that can find a large button is awake enough to use it.
If your alarm history shows it was dismissed at the right time and you have no memory of it, stop debugging your phone. The phone worked. The problem is that switching your alarm off was easy enough to do unconscious.
When the settings are all correct and you still sleep through
That last case is the one settings can't fix. UpRoar makes the off switch something a sleeping brain can't reach: speak a line aloud, solve fresh maths, walk to a code in another room. It also checks your alarm permissions for you and tells you exactly which ones your phone is quietly blocking.
Get UpRoar for AndroidA five-minute test worth doing tonight
Whatever alarm app you use, don't wait until morning to find out whether your fixes worked. Set an alarm for two minutes from now, lock the phone, put it face down and leave the room. If it doesn't ring loudly enough to hear from outside the door, nothing about tomorrow morning will be different.
Then repeat it with the phone unplugged and the screen off for ten minutes first — that's closer to what happens at 3am, and it's where battery optimisation problems actually show up.