Will an alarm app work when the iPhone is locked or the app is closed?
4 min read
We make an alarm app, and this page is written to be useful even if you never install it. The free fixes come first, because for most people they are enough. Anything about sleep itself is sourced to published research or the NHS rather than to us, and linked at the bottom. Mornio is not a medical product and cannot diagnose or treat anything.
Short answer
Yes to both. An alarm is scheduled with iOS rather than run by the app, so it fires with the phone locked and the app closed. You do not need to leave an alarm app open overnight.
What has historically broken third-party alarms is different: a restart, an app update, or a declined permission. Force-quitting from the app switcher can also matter for some implementations, so it is worth not doing.
A lot of people leave their alarm app open all night, phone plugged in and screen dimming, in the belief it is necessary. It is not, and understanding why tells you what to actually worry about.
How alarms are scheduled
When you set an alarm, the app hands it to iOS. From that moment the operating system owns it. The app does not need to be running, in the foreground, or open at all. This is why Apple's Clock alarms fire perfectly while your phone sits locked on a bedside table.
Since iOS 26, apps using AlarmKit schedule alarms the same way, which is the whole point of the framework. The alarm belongs to the system, not to the app.
So what does break alarms?
A declined permission. The most common cause by a distance. AlarmKit apps must ask permission to schedule alarms; decline it and nothing is scheduled, no matter what the app's interface shows.
A flat battery. The single most common cause of a missed alarm overall, and no framework fixes it.
A restart. Historically the weak point for notification-based alarms. Worth testing after a reboot.
An app update overnight. Also historically a failure point.
Force-quitting from the app switcher. With a system alarm this should not matter, but implementations vary, so it is a habit worth dropping.
Deleting the app, which obviously cancels everything.
The app being closed is not the risk. The permission, the battery and a restart are.
Should I leave the app open?
No, and it is mildly counterproductive. It uses battery, and battery is the actual risk. Set the alarm, lock the phone, plug it in, put it across the room.
The one thing worth doing instead is not force-quitting the app before bed. Swiping apps away from the switcher does nothing useful for battery on iOS anyway, and for alarms it introduces a variable you do not need.
The test that covers all of this
Set an alarm two minutes ahead.
Close the app fully and lock the phone.
Confirm it rings.
Now restart your iPhone, set another alarm two minutes ahead, and confirm again.
The second half is the one people skip and the one that catches the historical failure mode. Full walkthrough in how to test an alarm app.
For a morning that genuinely matters
Do all of the above, then add a second alarm on a different device with a separate power source. A mains-powered clock defeats a flat battery, which is the failure no software can address. That is not paranoia; it is what people catching early flights actually do.
Scheduled with iOS, not by the app
Mornio's alarms fire with the app closed and the phone locked. Test it in three minutes.
Yes. Alarms are scheduled with iOS rather than run by the app, so the app does not need to be open or running in the background. This applies to Apple's Clock and to third-party apps using AlarmKit. You do not need to leave an alarm app open overnight, and doing so only uses battery.
Will an alarm work when my iPhone is locked?
Yes. A locked screen has no effect on whether an alarm fires. With a system alarm you get a full-screen alert on the Lock Screen when it rings. The things that actually prevent an alarm firing are a declined permission, a flat battery, or in some historical cases a restart or overnight app update.
Does force-quitting an alarm app stop the alarm?
With a properly scheduled system alarm it should not, because the alarm belongs to iOS rather than the app. Implementations vary though, so it is a habit worth dropping. Swiping apps away from the app switcher does not help battery life on iOS anyway, so there is no benefit to offset the risk.
Do I need to keep my alarm app open overnight?
No, and it is slightly counterproductive since it uses battery, and a flat battery is the most common cause of a missed alarm. Set the alarm, lock the phone, put it on charge and place it across the room. Just avoid force-quitting the app from the switcher.
Sources
Apple, AlarmKit framework documentation, and Apple’s WWDC25 session “Wake up to the AlarmKit API”, on the iOS 26 framework that lets third-party alarms sound through Silent mode and Focus.
App Store details change without notice. Everything above was checked on 21 July 2026 — if you spot something out of date, tell us at support@mornioapp.com and we’ll correct it. Written and published by the Mornio team. Last reviewed 21 July 2026.