No. If your iPhone is powered off or the battery has died, the alarm will not go off, whether it's a Clock alarm or one from a third-party app. It does go off in Low Power Mode, Airplane Mode, silent mode and Do Not Disturb or other Focus modes, because those only change what the phone does while it's on.
So the one rule is: the phone has to be on and charged. Everything else is about volume and where the sound comes out. Here's the breakdown, then a checklist for mornings you can't afford to miss.
Short answer: which states ring
| iPhone state | Does a Clock alarm ring? | Notes |
|---|---|---|
| Powered off | No | A switched-off iPhone can't wake itself for an alarm. |
| Battery dead | No | Same as powered off. |
| Low Power Mode | Yes | Cuts background work, not alarms. |
| Airplane Mode | Yes | Alarms don't need a signal. |
| Silent mode (switch or Action Button) | Yes | Clock alarms ignore the silent switch. |
| Do Not Disturb / Focus (incl. Sleep) | Yes | Clock alarms ring through Focus modes. |
| Locked, screen off | Yes | The normal state for an alarm. |
| Restarting at the alarm time | Unreliable | Don't count on it. |
| Bluetooth headphones or speaker connected | Yes, but maybe not where you are | The sound may go to the connected device. |
That's for the built-in Clock app. Third-party apps are covered below.
Off or dead: why the alarm can't ring
Some old phones could switch themselves on for an alarm, which is where the myth comes from. iPhones don't. When an iPhone is shut down, nothing is running that can power it up and play a sound at 6:30.
A dead battery is the same. Some recent iPhones keep a small power reserve after shutting down for things like finding a lost phone, but alarms aren't part of that.
This catches people in predictable ways:
- The phone was at 9% at bedtime and didn't make it, especially with an older battery.
- The charger wasn't really charging. A loose cable, a tired adapter, a phone slightly off-center on a wireless charger, or a power strip switched off.
- They turned the phone off to rest properly and assumed the alarm would still work.
- Battery health is poor, so the charge drops fast overnight, and faster in the cold.
Low Power Mode: yes
Low Power Mode reduces things like background app refresh, automatic downloads and some visual effects. It doesn't disable Clock alarms. On a low-battery night it's your friend, because it makes it more likely the phone lasts until morning. Turn it on in Settings > Battery > Low Power Mode or from Control Center.
Airplane Mode: yes
Alarms run on the phone's own clock, with no network involved. That's why Airplane Mode is a good overnight setting in a hotel or on a red-eye: fewer interruptions, less battery drain, and the alarm still rings.
One thing to check when travelling: alarms go off at the local time the phone shows. If the phone hasn't updated to a new time zone, your alarm will be off by the difference. Look at the lock screen clock before bed. More in how to wake up for an early flight.
Silent mode, Do Not Disturb and Focus: yes
Clock alarms ring out loud through the silent switch and every Focus mode, including Do Not Disturb and Sleep. That's deliberate, and it's explained in does the iPhone alarm work on silent.
What actually takes the sound away is usually one of these:
- The alarm's Sound is set to None.
- Ringer and Alerts in Settings > Sounds & Haptics is near zero.
- AirPods or a Bluetooth speaker took the audio.
What about third-party alarm apps?
It depends on the app. One that only sends notifications follows your notification rules, so a Focus mode can silence it and low alert volume can make it quiet. On recent iOS versions (iOS 26 and later), Apple's AlarmKit lets third-party apps schedule system-level alarms that behave more like the Clock app.
What no app can do is ring from a phone that's off or dead. Captain Wake keeps ringing if you force-close it, restart the iPhone or turn the volume to zero, and only stops when you complete a mission. But it needs power like everything else, so the checklist still applies.
The night-before checklist
For an exam, an interview, a flight or a first shift:
- Charge it. Plug in and check the charging icon appears.
- Don't power it off. Use Airplane Mode or a Focus mode for quiet. Never shut down.
- If you can't charge, turn on Low Power Mode and close battery-hungry apps like navigation.
- Check the alarm. Right time, AM/PM, toggle on, right days, Sound not None.
- Check the volume in Settings > Sounds & Haptics and tap the slider to hear it.
- Disconnect Bluetooth audio. AirPods in their case with the lid closed, or Bluetooth off.
- Don't update overnight. Install pending iOS updates in the evening and test an alarm afterwards, or wait until after your big morning.
- Set a backup. A second alarm 10 minutes later or a cheap standalone clock. See how many alarms you should set.
When the phone rings but you still sleep through it
If the phone was on, charged and loud and you still missed the morning, the problem isn't power. You slept through the sound or switched it off without really waking, and more volume rarely fixes that. Mission alarms are designed for exactly this: Captain Wake asks you to do something that needs you awake, like photographing your bathroom sink or scanning a barcode in the kitchen, before it goes quiet.
Who this is NOT for
- If your phone shuts down with charge left, that's a battery or hardware issue. Check Settings > Battery > Battery Health and contact Apple Support.
- If your alarm doesn't fire even when the phone is on, see iPhone alarm not going off.
- If you need the phone off at night, use a dedicated alarm clock.
The takeaway
Off or dead means no alarm. Low Power Mode, Airplane Mode, silent mode and Focus modes all still ring. Before a morning that matters, charge the phone, leave it on, check the volume and audio route, and set one backup.
