Why do I sleep through my alarm?
Why do I sleep through my alarm? Five causes, and what to change tonight.
Most people who sleep through an alarm are not broken sleepers. They are short of sleep, or the alarm landed in deep sleep, or the phone was quieter than they thought.
In order of likelihood: you did not get enough sleep; the alarm fired while you were in deep sleep, which is most of the early night; you are a naturally deep sleeper and sound alone does not reach you; the phone silenced or quietened the alarm; or something medical or chemical is in the way. Each has a different fix. Below: how to tell which cause is yours, a table matching each cause to its fix, the exact phone settings on iPhone and Android, and a ten-minute checklist for tonight. The facts are from the CDC, the US National Heart, Lung, and Blood Institute, a 2010 study in Current Biology, and Apple's and Google's own support pages, all read on 27 October 2026.
The five causes
Which one is yours
1. Not enough sleep
Looks like: you slept through it on a night you went to bed late, and woke fine on nights you did not.
The number: adults aged 18 to 60 need seven or more hours, by the American Academy of Sleep Medicine's recommendation as published by the CDC; 13- to 17-year-olds need eight to ten. An alarm set seven hours after lights-out gives you less than seven, because falling asleep takes time.
2. The alarm landed in deep sleep
Looks like: you woke eventually, confused, with no memory of the alarm, usually after going to bed much later than normal.
The mechanism: sleep runs in cycles of 80 to 100 minutes and the deep stage comes mostly early in the night, according to the NHLBI. Go to bed at 2 am and a 6 am alarm meets a brain still doing its early-night deep sleep. The fix is the bedtime, not the alarm.
3. You are a deep sleeper
Looks like: this has always happened, even after full nights, and other people in the house hear your alarm before you do.
The evidence: a 2010 study (Dang-Vu and colleagues, Current Biology) found that people who produced more sleep spindles, a brain rhythm of light sleep, tolerated more noise without waking. Some brains filter sound well. You cannot change that; you can change the wake method so that it is not sound alone.
4. The phone, not you
Looks like: the alarm "did not go off", or it went off and was too quiet to notice.
The settings: on iPhone the alarm sounds even in Silent mode or a Focus, but its volume is set separately under Sounds & Haptics. On Android, Do Not Disturb can silence an alarm unless alarms are allowed, and an alarm will not go off at all if the ringtone is set to silent with vibration off. Details and sources in the checklist below.
5. Something else is in the way
Looks like: you are sleepy most days, you sleep through alarms after full nights, a new medicine started, or evenings involve alcohol.
What to do: this is the one cause an alarm cannot fix. The NHS lists persistent daytime sleepiness as something to see a GP about. Take the two-week log from the bottom of this page with you.
Match the cause to the fix
If this, do that
| If | Then | Not this |
|---|---|---|
| Short nights are the nights you sleep through | Move bedtime, not the alarm. Count back seven hours from the alarm, then another 20 minutes for falling asleep. | A louder alarm. It wakes the house and not the problem. |
| Bedtime drifts later through the week | Fix the wake time first and keep it on weekends; the bedtime follows within a week or two. | Catching up on Sunday, which moves the clock the wrong way for Monday. |
| Full nights, still sleep through, always have | Change the wake method: vibration under the pillow, a full-screen light, and an alarm that ends only when you stand up and do something. | A second and third alarm in bed. You will learn to sleep through those too. |
| "It did not go off" | Run the phone checklist below tonight, then test the alarm one minute ahead at the real volume. | Assuming the last update left your settings alone. |
| Sleepy most days, or it started with a medicine | GP. Bring the log. | Another app. |
Tonight
A ten-minute checklist before you sleep
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Do the arithmetic
Alarm time minus seven hours minus twenty minutes is lights-out. If that is earlier than you can manage tonight, cause 1 is in play tomorrow whatever else you do.
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iPhone: check the alarm volume, not the ringer
Apple's "Set an alarm" page says the alarm sounds even in Silent mode, Do Not Disturb or any other Focus, and through headphones. Volume is under Settings, Sounds & Haptics, Alarms and Timers: if Match Ringtone Volume is off, drag that slider up; if it is on, your ringer volume is your alarm volume.
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Android: allow alarms in Do Not Disturb and check the alarm slider
Google's Clock help says Do Not Disturb can silence an alarm unless alarms are allowed in its settings, that the alarm will not go off if the ringtone is silent and vibration is off, and that the app warns when alarm volume is below 30%. Alarm volume is its own slider, separate from media and ring volume. On Android 14 and later, Settings, Modes, the mode you use at night, Notification filters, "Alarms and other interruptions".
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Put the thing that ends the alarm where you have to stand
Phone across the room is the oldest fix and it works without any app. If you have slept through that too, the alarm needs to end only when you do something a sleeping person cannot: scan a code in the hall, for example. See an alarm that makes you get up for placement.
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One alarm, tested
Delete the backups. Set the one alarm for one minute from now, at tonight's volume, with the phone where it will be, and let it ring. If you would not have heard that from under a duvet, change something now. Charge the phone where it will ring.
Find the cause
The two-week log
Three columns, fourteen rows, on paper or in a note: lights-out time, alarm time, and what happened (woke on first ring, woke late, slept through, phone problem). After two weeks the pattern reads itself. Slept through only on nights under seven hours: cause 1 or 2, fix the bedtime. Slept through on full nights too: cause 3, change the method. Phone problems: cause 4, done. Slept through on full nights and sleepy by day: cause 5, take the log to the GP, who will want exactly these numbers.
ProveAwake, the app made by the people behind this page, keeps this log for you as a Wake Record: each morning records which signals fired, which Awake Check ended the alarm, when, and whether you used Override. The QR Wake Point is its answer to cause 3, an alarm that ends only when you scan a code you placed away from the bed, and the Readiness Check is its answer to cause 4, firing every signal on your real phone the evening before. The wake-up, the QR check, the Readiness Check and Wake Records are in the free tier on the App Store and Google Play. It does not change how much sleep you need, and it cannot fix causes 1, 2 or 5; the bedtime and the GP are yours.
When this page is not enough
If you are sleepy most days, fall asleep without meaning to, or keep sleeping through alarms after seven or more hours in bed for two weeks running, stop adjusting alarms and see a doctor. The NHS page on excessive daytime sleepiness, linked below, lists the things a GP will consider, from sleep disorders to medicines. Waking up hard for 15 to 30 minutes after a very short sleep is normal sleep inertia, as the US NIOSH describes it, not a condition. Nothing here is medical advice, and no alarm, including ours, can promise to wake every person every morning.
Questions
Common questions
Why am I suddenly sleeping through my alarms?
Something changed. Check in order: bedtime drifted later, so the alarm now lands in deep sleep; a phone update or a new Focus or Do Not Disturb mode changed what the alarm may do; a new medicine or more alcohol in the evening; or sleepiness that has crept up over weeks, which is a GP question.
Is sleeping through alarms a sign of ADHD or a sleep disorder?
This page cannot tell you, and neither can an app. After a short night it is ordinary. After full nights, week after week, or with sleepiness most days, it is the pattern to take to a GP.
Should I set several alarms?
One you cannot end from the pillow beats six you can. If you want a second chance, make it a recheck after you are up, not another ring in bed.
Sources
CDC: About Sleep (recommended hours by age, from the American Academy of Sleep Medicine). NHLBI: Sleep phases and stages (80- to 100-minute cycles; deep sleep early in the night). Dang-Vu et al., 2010, Current Biology (sleep spindles and noise tolerance). Apple: Set an alarm in Clock on iPhone. Google: Set, cancel or snooze alarms. CDC/NIOSH: Nap duration and sleep inertia. NHS: Excessive daytime sleepiness. All read on 27 October 2026.