Why some people sleep through alarms
Sleep is not one depth all night. Deep sleep, the stage that is hardest to wake from, is concentrated in the first part of the night, and lighter sleep and REM take over towards morning. An alarm that goes off during deep sleep meets the highest arousal threshold of the night, and the grogginess after waking from it (sleep inertia) is at its worst.
Short sleep makes it worse. After nights that were too short the body claws back deep sleep, so more of the morning is spent in the stage that is hardest to wake from. A pattern of sleeping through alarms is often a pattern of not sleeping enough.
The other half is behaviour: silencing an alarm is a reflex you can perform asleep. Many people who "never heard" the alarm did hear it, and stopped it without remembering.
What actually works
- Make stopping it take thought. An alarm that needs a task (standing up, finding something, a photo, a code) beats a louder one, because the reflex that silences it never fully wakes you.
- Keep it going. One ring is easy to miss; an alarm that rings again every few minutes until you are demonstrably up is not.
- Start before the time you must be up. A gentle first ring 15 to 30 minutes early catches lighter sleep, so the loud one at the real time meets someone already halfway awake.
- Limit the snooze, don't ban it. A fixed number of short snoozes keeps the choice without letting it run the morning.
- Same wake time every day, weekends included. A steady rhythm moves deep sleep away from your alarm time.
- Light, early. Daylight or bright light right after waking cuts sleep inertia and pulls tomorrow's sleepiness earlier.
Setting it up on iPhone
Alarms made in the Clock app, and in apps that use Apple's alarm system (AlarmKit, iOS 26 and later), ring even with the phone on silent and through a Focus. Check the volume under Settings, Sounds and Haptics: alarms follow the ringer and alerts volume. An ordinary app notification is not an alarm: it can be silenced by a Focus and is easy to miss.
How Life OS does it
Life OS has a Wake me up no matter what switch at the top of the Alarm screen. It starts ringing before your wake time, keeps ringing until you are up, and on Pro your ELO phones you at the wake time and every three minutes after until you are. Sleep more replaces snooze: you choose how many and how long, and when they are gone the button says I'm up. For the hardest mornings there is an alarm you can't dismiss without getting up and photographing something.
Questions people ask
Why can't I wake up to my alarm?
Usually because it goes off during deep sleep, which is hardest to wake from and is heavier after short nights, and because silencing an alarm is a reflex you can do half asleep. An alarm that starts earlier, keeps going and needs a deliberate action to stop works far better than a louder one.
Does an iPhone alarm go off on silent?
Yes. Alarms from the Clock app, and from apps using Apple's AlarmKit on iOS 26 and later, ring with the phone on silent and through Focus modes. Their loudness follows the ringer and alerts volume in Settings.
What is the best alarm for heavy sleepers?
One that rings early and then keeps going until you are actually up, limits snoozing, and needs a deliberate action to stop. Loudness alone helps less than people expect.