Posted on Jan 28, 2010

How Does Sleep Cycle Work?

Sleep seems to be a reoccurring topic here (see my previous post on good sleeping habits), which isn’t surprising seeing as it’s such an interesting subject, even more so when it’s related to technology. Tommy Collison wrote a great post this week about an iPhone app called Sleep Cycle Alarm Clock that helps you wake up more naturally and since trying it out I’ve been acutely aware of the scepticism online surrounding its validity and usefulness.

Sleep Cycle is an app that turns you iPhone into a bio-alarm clock. Using the accelerometer built into the iPhone it reads specific movements common during sleep and wakes you up when you are sleeping lightly, aiming to give you a more refreshing awakening. Haven’t we all felt the frustration of being woken up during an especially interesting dream, and then felt dreadful for the day because of it?

This type of movement based bio-alarm clock has been around for awhile. You often find them as glorified watches with internal accelerometers, or overcomplicated devices that require placing motion detecting electrodes under your pillow case. The reason bio-alarm clocks work is due to the extensive sleep research that tells us how our body moves or doesn’t move during sleep.

How Does It Work?

Software like Sleep Cycle looks out for the right breathing patterns or muscle activity to determine what stage of sleep we are at. For example, during the REM stage of sleep (when we are dreaming) your body is essentially paralysed, this stops your body from acting out and hurting itself during a dream, but during light sleep your muscles will occasionally twitch. Another example is how during the deepest stage of sleep your breathing becomes rhythmic, but during REM sleep your breathing is rapid and shallow. These are distinct and measurable differences and are the biological indicators that bio-alarm clocks are looking out for.

The Sleep Cycle app on the iPhone doesn’t just wake you up though; it also produces a graph of your sleep pattern, so you get a general idea of how restful your sleep was. These graphs are more of a novelty than anything else and though I wouldn’t recommend you use them to make inferences about how healthy your sleeping behaviour is, it could provide you with a valuable insight when paired with keeping track of your routines, helping you to figure out what works best for you for a good night’s sleep.

Sleep Cycle alarm clock - Maciek Drejak Labs


  • Eoin Redmond says:

    Hey Sinead,

    I used this app for the first time last night with mixed results.

    Firstly, it does show your sleep pattern which is very interesting. I really look forward to the nights I go sleep walking now.

    However, unlike a conventional alarm that you have set for 8am, allowing 15 minutes of snooze time, the Sleep Cycle builds these snooze minutes into the time you’ve set. The Sleep Cycle alarm went off at 7:30, 45 minutes before I planned to get up!! I instinctively turned it off and then didn’t wake till 9am!

    My warning to anyone beginning to use the Sleep Cycle Alarm, is learn from my lesson and don’t make a Friday after a long week the first morning you rely on it.


  • Sinéad says:

    It’s true that the app doesn’t allow for any snooze time, but that’s the whole point of the app, you’re supposed to get up exactly when it tells you otherwise you might fall back asleep and into another REM cycle. I set it for 7am and it usually wakes me between 6.45 and 7.15, so the margin of error is 30mins.

  • Hey Sinead,

    I downloaded this app ages ago but never used it. Can’t say i like the idea of being woken up by the iPhone’s AI of my sleep patterns. Best clock i know of is the sun (& a open curtain!)

    Might give this another try…


  • Sinéad says:

    I think if I relied on the sun to wake me up here in Ireland I’d be getting FAR too many lie-ins! :)

  • Jennifer says:

    Hey Eoin,

    You are using it wrong. The app is designed to wake you up when you are in your lightest sleep so you wake up refreshed. If you had waited another 30 minutes you may have been in a deep sleep cycle, and then you would wake up feeling groggy.

  • kath says:

    works great! I get up refreshed in the mornings which is unusual for me. Am looking forward to seeing the graph and what it says compared with the type of sleep I got. I always thought it took me ages to get back to sleep if woken at night. Turns out it just feels that way!