Alarm Doesn't Ring When Your Phone Is Locked? Here's the Chain That's Breaking

This failure has a very specific and very maddening shape: you test the alarm with the phone in your hand and it's perfect. You lock the phone, go to sleep, and get either total silence, a feeble notification chirp, or — strangest of all — sound with a black screen you can't dismiss without unlocking. We build an alarm app, and internally we call this the "rings but no screen" bug class; it's been one of our biggest engineering battles since Android 14. Here's what breaks, ranked by how often we see it, and how to fix each link in the chain.

How a locked-phone alarm is supposed to work

Three things must happen in sequence at 7:00 a.m. on a locked, sleeping phone:

1. The trigger fires. The app must have registered the alarm through Android's setAlarmClock() API — the only mechanism guaranteed to fire on the second even in Doze deep sleep. (Bonus: it puts the little alarm icon in your status bar.)
2. The process wakes. The system starts the app so it can play sound — unless a battery manager has decided the app may not run.
3. The screen takes over. The app posts a full-screen intent that lights the display and shows the ring screen over the lock screen — a privilege Android 14+ no longer hands out automatically.

Your symptom tells you which link broke. Silence = link 1 or 2. Sound but no screen, or a quiet notification = link 3.

Cause 1: The full-screen intent permission is missing (Android 14+)

Since Android 14, the OS gates the full-screen alarm experience. Apps installed before the change, or apps the system doesn't recognize as alarm apps, can lose the right to take over your screen — and the alarm silently degrades into a notification. This is the single most common cause of "it used to work and stopped after an update."

Fix:

1. Open Settings → Apps → Special app access → Alarms & reminders → allow your alarm app.
2. Open Settings → Apps → [alarm app] → Notifications and confirm the alarm channel is enabled, not silenced, and — where your phone shows it — allowed to use full-screen notifications.
3. Reboot once after changing these; some phones apply full-screen grants lazily.

Cause 2: A battery manager killed the app before morning

If the process is dead and forbidden from restarting, no permission matters. Stock Android's Doze usually respects real alarms; manufacturer skins often don't. Xiaomi/MIUI is the harshest (Autostart off by default), with some Samsung and OnePlus power modes close behind.

Fix: set the app's battery use to Unrestricted (Settings → Apps → [app] → Battery). Then apply your brand's specifics: the MIUI checklist (Autostart, No restrictions, lock in recents) or the Samsung sleeping-apps fix. The full background is in battery optimization killing alarms.

Cause 3: OEM lock-screen permissions (mostly Xiaomi)

MIUI/HyperOS adds its own gate on top of Android's: per-app permissions called "Show on lock screen" and "Display pop-up windows while running in the background." Without both, the ring screen cannot appear on a locked phone no matter what Android itself allows. Find them under Settings → Apps → Manage apps → [alarm app] → Other permissions.

Cause 4: The sound is being blocked separately

Sometimes the screen part works and the audio is the missing half — which feels like "doesn't ring when locked" from under a blanket. Two usual suspects: the alarm volume stream is near zero (it's a separate slider from media — see alarm volume too quiet), or Do Not Disturb is configured without the alarms exception (see DND blocking alarms).

Cause 5: The app schedules alarms the wrong way

Everything above can be perfect and the alarm still fails if the app itself uses inexact scheduling — ordinary background jobs get batched and deferred in Doze, sometimes by hours. You can't fix this in settings, but you can detect it: after setting an alarm, look for the alarm-clock icon in your status bar. Registered via setAlarmClock(), it's there; scheduled some other way, it usually isn't. If a specific app repeatedly fails on a phone where the built-in Clock is punctual, the app is the problem.

The verification test

1. Set an alarm 15 minutes out.
2. Lock the phone and put it face-up across the room. Don't touch it — a lit screen or open app skips the exact code path you're testing.
3. Pass = on-time sound at full alarm volume and a ring screen over the lock screen you can dismiss without unlocking.

Run it once more after the phone has idled for a few hours if your failures happen only on real mornings — that's the battery-killer timescale. And if the alarm rings properly but you stay asleep, the fix is different: see heavy sleeper alarm tips.

FAQ

Why does my alarm only work when my phone is unlocked?

Because ringing on a locked phone requires more privileges than ringing on an unlocked one. The app must be allowed to schedule exact alarms (Alarms & reminders access), to show a full-screen screen over the lock screen (gated since Android 14), and its process must survive Doze and any manufacturer battery killer. When the phone is unlocked and the app is open, none of those gates apply — which is why the failure only shows up locked.

What is a full-screen intent and why does my alarm need it?

A full-screen intent is the Android mechanism that lets an alarm or incoming call take over the whole screen, even over the lock screen. Since Android 14, apps can no longer assume this privilege — it's a special permission the system or user must grant. Without it, the alarm degrades into a regular notification: it may vibrate or chime briefly, but no ring screen appears, and it's easy to sleep through.

Do alarms normally ring when the phone is locked?

Yes — a correctly built and correctly permissioned alarm app rings on a locked phone, lights up a full-screen alarm over the lock screen, and does so even in deep sleep. Android's setAlarmClock() API exists precisely for this and fires even in Doze. If that isn't happening, a permission or battery setting is blocking it, or the app is scheduling alarms the wrong way.

How do I check the Alarms & reminders permission?

Open Settings → Apps → Special app access → Alarms & reminders, and make sure your alarm app is allowed. On some phones the same screen is reachable from the app's own info page under "Alarms & reminders." While you're there, also check the app's notification settings — the alarm channel must not be silenced — and its battery setting, ideally Unrestricted.