You set an alarm, you confirm it is on, you go to sleep, and you wake up late because the alarm never went off — or it went off so quietly you slept through it. This is a surprisingly common problem on both iPhones and Android phones, and it is almost always a settings issue rather than a broken phone. The alarm system interacts with volume controls, Do Not Disturb mode, Bluetooth audio routing, and battery optimization in ways that are not obvious, and any of these can silently prevent your alarm from working as expected.
Check the alarm volume (it is separate from your ringer)
This is the most common cause. Alarm volume and ringer volume are handled differently depending on the phone:
iPhone
By default, the volume buttons on the side of the iPhone control the ringer and alert volume, which includes alarms. If you turned the volume all the way down before bed (to silence notifications), you also turned down the alarm volume. Check:
Go to Settings, Sounds and Haptics
Look at Ringers and Alerts — the slider should be at a comfortable volume level, not all the way to the left
Below the slider, there is a toggle: Change with Buttons. If this is on, the physical volume buttons affect alarm volume. If you tend to lower volume before bed, turn this setting OFF so alarm volume stays fixed regardless of the volume buttons
Android
Android separates media volume, ringtone volume, and alarm volume into three independent sliders:
Press a volume button, then tap the three-dot menu or the slider icon to expand all volume sliders
Find the Alarm volume slider (usually shown with a clock icon). Make sure it is turned up
Alternatively, go to Settings, Sound and vibration, and adjust the Alarm volume there
Because Android separates these volumes, you can set media and ringtone to zero for a quiet night while keeping alarm volume at maximum. Many people do not realize these are independent controls.
Check Do Not Disturb settings
Do Not Disturb (DND) mode is designed to silence notifications and calls, but it can also affect alarms depending on the configuration:
iPhone
The built-in Clock app alarms should sound even when DND or a Focus mode is active — this is the default behavior. However, if you are using a third-party alarm app, DND may silence it because third-party apps are treated as regular notifications. If you use a third-party alarm app, either switch to the built-in Clock app or add the alarm app to your Focus mode's allowed apps list (Settings, Focus, select the mode, Apps, add the alarm app).
Android
Android's DND mode has an explicit setting for alarms:
Go to Settings, Sound and vibration (or Notifications), Do Not Disturb
Look for Alarms and other interruptions (or Exceptions depending on the manufacturer)
Make sure Alarms is toggled ON. If it is off, DND silences everything including alarms
Samsung phones have an additional Bedtime mode in the Clock app that dims the screen and silences notifications. Check that alarms are allowed within Bedtime mode settings as well.
Check that the alarm is actually set correctly
This sounds obvious, but these are common mistakes:
AM vs PM. Setting an alarm for 7:00 PM instead of 7:00 AM is easy to do and hard to notice, especially when setting alarms in a hurry at night. Double-check the AM/PM indicator. If your phone uses 24-hour time, this is not an issue — 07:00 is morning, 19:00 is evening
Wrong day. Repeating alarms set for specific days (weekdays only, for example) will not go off on Saturday or Sunday. If you set a one-time alarm, make sure it is set for tomorrow's date and not today (an alarm set for a time that has already passed today will wait until the next day on some phones and silently expire on others)
The alarm is toggled off. Open the Clock app and verify the toggle next to your alarm is ON (usually shown in green or blue). It is easy to accidentally swipe an alarm off while handling the phone
Multiple alarms interfering. If you have many old alarms saved, one that you thought was your active alarm may be disabled while a different one (set to the wrong time) is enabled. Delete old alarms you no longer use to reduce confusion
Check Bluetooth audio routing
If your phone is connected to a Bluetooth speaker, headphones, or a car's Bluetooth system, the alarm audio may be routing to that device instead of the phone's speaker:
Bluetooth earbuds left in a case that does not fully disconnect can still receive audio
A Bluetooth speaker in another room (or powered off but still paired) can sometimes capture the audio output
Disconnect Bluetooth before bed or check that the alarm app is set to play through the phone speaker. On iPhones, the built-in Clock alarm always plays through the phone speaker regardless of Bluetooth — but third-party alarm apps may not
Battery optimization (Android)
Android's battery optimization features aggressively manage background apps to save power. If the alarm app is being optimized, the system may prevent it from running in the background, which means it cannot trigger the alarm:
Google Clock app: Should be exempt from battery optimization by default. But on Samsung, Xiaomi, Huawei, OnePlus, and other manufacturers with custom battery management, even the default clock app can be restricted. Go to Settings, Apps, select your clock or alarm app, Battery, and set it to Unrestricted (not Optimized or Restricted)
Third-party alarm apps: These are more likely to be killed by battery optimization. The same fix applies — set the app to Unrestricted in battery settings. On Samsung, also check Settings, Battery and device care, Battery, Background usage limits, and make sure the alarm app is in the Never sleeping list
Adaptive battery. Settings, Battery, Adaptive battery — this feature learns which apps you use infrequently and restricts them. If your alarm app is not the built-in Clock app, adaptive battery may eventually restrict it
Software-specific issues
Alarm tone set to None. Check the alarm settings and make sure a sound is selected. On iPhones, if the alarm tone is set to None, only vibration occurs (and if vibration is also off, nothing happens at all). On Android, check both the alarm tone and vibration settings
Bedtime/Sleep mode interaction. Both iPhone (Sleep Focus) and Android (Bedtime mode) have sleep-specific modes that can modify alarm behavior. On iPhone, the wake-up alarm is set within the Health app's Sleep schedule, separate from the Clock app — if you are relying on the Sleep schedule alarm, check Health, Sleep, Full Schedule and Alarm
App needs updating. If you are using a third-party alarm app, an outdated version may have bugs that prevent alarms from triggering. Update the app from the App Store or Play Store
Restart the phone. A restart clears any software state that may be interfering with alarm scheduling. If your alarm has failed to go off more than once, restart the phone and reset the alarm
When the phone itself is the problem
Rarely, alarm failure is a hardware or deeper software issue:
Speaker damage. If the phone's speaker is physically damaged (blown out, water damage, debris-clogged), the alarm may be triggering but producing no audible sound. Test by playing music or a ringtone at full volume. If no sound comes out, the speaker needs repair
Phone shutting down overnight. A phone with a failing battery may shut down during the night when the battery level drops too low. If you wake up to a dead phone, the alarm obviously could not go off. Charge the phone overnight or have the battery checked if it cannot hold a charge
Alarm troubleshooting at Marion Phone Repair
Marion Phone Repair diagnoses alarm and audio problems — whether the issue is a software setting, battery optimization conflict, or hardware problem like a damaged speaker or failing battery. We test the alarm system and speaker output before returning the phone.