Sleeping through your alarm? What actually wakes heavy sleepers
Most people do hear the alarm. What keeps heavy sleepers in bed, which sounds woke people best in sleep-lab tests, and what to try when nothing works.
Do heavy sleepers really not hear the alarm?
Usually they do. The clearest test comes from research on smoke alarms. In a study in Ohio, 150 healthy adults aged 20 to 49 slept in a lab bedroom. Each was woken from deep sleep by four different alarms, played at 85 decibels at the pillow.[1]
All but one woke up to all four alarms and walked out of the room. The one exception slept through the high-pitched beep. Median time to wake: 2 seconds for the high-pitched alarm, 1 second for the others.[1]
So why does it so often feel like the alarm never rang? A common answer is that you did wake, switched it off, and fell asleep again. And you may not remember. In a lab study on memory at sleep onset, people who then slept for 10 minutes had great trouble recalling word pairs they had heard in the three minutes before falling asleep. After only 30 seconds of sleep, the same gap did not appear.[9]
That fits a familiar morning: an alarm you silenced and slept through can feel like one that never went off. It also means the second problem, staying up, deserves as much attention as the first.
What makes you harder to wake?
Deep sleep. The deeper the sleep, the louder a sound has to be to wake you. In a lab study with 10 men, researchers kept them out of deep sleep for two nights. On the recovery night they got more deep sleep, and it took a louder tone to wake them. The same study found that the sound needed to wake someone fell steadily over the course of the night.[2]
Too little sleep, and other risks. A review of emergency-awakening research lists what makes people likely to stay asleep: high background noise, being a heavy sleeper, sleep deprivation, being a child, sleeping pills, alcohol, and hearing loss.[3]
Waking at the wrong time for your body clock. A clinical review describes people whose body clock runs late, who would sleep from 3 a.m. to 11 a.m. if they could but must get up at 8. The review names two likely reasons why waking is so hard for them: built-up sleep debt, and a body clock that is still set to sleep.[8]
Which alarms wake people best?
Most of what we know comes from smoke-alarm studies, where the stakes are high and waking is measured precisely. The results are consistent on a few points.
| What wakes you | What the studies found | Evidence |
|---|---|---|
| A low-pitched beep | In 39 young adults in deep sleep, low-pitched square-wave beeps (400 and 520 Hz) woke people at lower volumes than the alternatives.[4] In adults with hearing loss, the 520 Hz beep woke 92%, the usual high-pitched alarm 56%.[5] | Strong evidence |
| A human voice | Children: a recorded voice woke 86 to 91%, a high-pitched tone 53%.[6] Healthy adults: a voice woke them as fast as a low-pitched tone.[1] | Some evidence |
| Hearing your own name | Adding the child’s first name to the voice message woke no more children than the same message without it.[6] | Some evidence |
| A bed or pillow shaker | Woke 80 to 84% of adults with hearing loss, at the strength they came with.[5] | Some evidence |
| A flashing light | Woke 27% of adults with hearing loss, even brighter than the US standard.[5] In another study, strobes did not wake people reliably even with the light right above their face.[7] | Some evidence |
Two caveats. These are emergency signals, tested once, mostly in the deepest sleep of the night. Since the sound needed to wake people falls over the course of the night,[2] a morning alarm has an easier job than these tests. And what wakes you fastest is a different question from what leaves you least groggy afterwards. For grogginess, there is not enough evidence in adults to say which alarm sound works best:[10] sleep inertia, explained.
Hearing it is half the job. Staying up is the other half
If you wake to the alarm but find yourself back in bed, a louder sound won’t fix that. What helps is making the off switch, or the minutes after it, need an awake brain.
There are no studies on alarms that make you solve a task before they stop, or that check on you again a few minutes later. The idea follows from the research above, though. If the trouble is switching off half asleep and drifting off within minutes, then anything that keeps you up for those minutes targets the actual problem. The simplest version costs nothing: put the alarm where you have to stand up to reach it.
And the snooze button? The research is small and split. In a Swedish lab study with 31 habitual snoozers, half an hour of snoozing did no harm to their test results;[11] in a Japanese lab study with 10 students, the snooze alarm prolonged the morning fog.[12] More on both in our article on sleep inertia.
When it is more than being a heavy sleeper
There is also a rarer cause. Idiopathic hypersomnia is a neurological sleep disorder: daytime sleepiness despite long nights, sleep that doesn’t refresh, and great difficulty waking up.[8] Nearly half of patients have what doctors call “sleep drunkenness”, a waking far heavier and longer than the normal morning fog.[8]
If you regularly sleep through very loud alarms, sleep long and still feel sleepy during the day, it is worth seeing a doctor. The diagnosis rests on your history and on objective sleep tests.[8]
