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Alarm Clocks

Alarm clocks have become an ingrained part of our everyday lives. If you need to get up to go to work, school or university, you will likely make use of an alarm clock rather than run the risk of sleeping in. However, you may not have considered the implications that the use of an alarm clock can have on your sleep cycle and general quality of sleep.


Alarm Clocks

When we sleep we go through various phases, from light sleep (stage NREM1 and NREM2) to deep sleep (slow-wave sleep), and this happens in cycles, meaning we will experience each phase numerous times during the night. With natural sleep, not using an alarm clock, you will usually wake up when in a lighter stage of sleep, meaning the transition from sleeping to waking is relatively easy.

On the other hand, being waken up during deep sleep can make you feel very groggy and lead to a feeling known as ‘sleep inertia’. Sleep inertia impairs your focus and alertness and can make it difficult to carry out simple tasks. If you feel like this on a morning it may be that your alarm clock is waking you during slow-wave sleep, when your body is physically unprepared for being awake.

There are alarm clocks available (and some smartphone apps) to help you with this issue, designed to recognise when you are in a lighter stage of sleep, avoiding alerting you from a deep sleep and making the process of waking up much easier. They generally use sensors to detect when you make the most movement during the night (suggesting that you are in a lighter stage of sleep and therefore more easily woken), meaning you can still wake up in time for work or school, but without suffering from a sudden, inopportune awakening.

If you are not able to use one of these sleep cycle alarms, you can measure your sleep cycle manually, but this would only ever be a rough estimate and may still leave you feeling groggy. Sleep cycles typically last ninety minutes, and five to six cycles will give you a restorative night’s sleep.


  • Alarm clocks are fine to use, but may wake you during deep sleep.
  • Waking during deep sleep can cause sleep inertia, making you feel sluggish and groggy.
  • Waking up during a lighter stage of sleep, whether through using a sleep-cycle alarm or not, will allow you to feel much more alert and refreshed on a morning.

Using an alarm clock is perfectly fine, and will not have any adverse effect on your quality of sleep if it wakes you during a lighter stage of sleep. However, if you can allow yourself the amount of sleep that your body needs to feel fully refreshed, then you are more likely to wake up naturally without the need for an alarm. If you are scared of being late, then simply use an alarm clock as a back-up, setting it to go off fifteen minutes after you are planning to naturally wake up.

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