Sleep Cycle: Review of iPhone Alarm App

I've spent the last week playing around with a 99 cent iPhone/i Pod Touch application called Sleep Cycle.  This is one of the innovate ways to incorporate the device accelerometer to monitor motion during sleep.  Motion during sleep is a proxy for sleep stage:  the more motion you are creating suggests being awake or in a light stage of sleep.  Deep sleep (or stage 3 or 4 sleep) typically involves limited movement.  REM (rapid eye movement) sleep that typically includes dream sleep also involves very limited physical body movement.  


Sleep cycle is a software app that uses movement during sleep to time your iPhone alarm.  It is designed to reduce the likelihood that your alarm will go off during a period of deep sleep or REM sleep.  If you have some movement around the time your alarm is set to go off, the alarm will be set off.  So say you want to wake up no later than 7 am.  Beginning at 630 am, sleep cycle with monitor physical movement.  If you begin to move during that 30 minute window, the alarm will sound.  I found the app easy to use and the primary function worked well--each time the alarm went off I was easily able to hear it and didn't feel like I had been awakened from a deep sleep or during dreaming.


But what I found even more fascinating than the alarm function with this app is the plot function that allows you to look at the entire night pattern of physical motion plotted to estimated sleep stage status.  The top screen shot shows a plot from my trial with the app.  It shows I fell asleep quickly to a deep sleep state.  I was awake at around 2 am for a brief period of time (elderly men will know what this was about) and then fell asleep with a gradual increase in sleep movement until being awakened by the alarm.  This pattern is pretty typical for normal patterns seen with more advanced sleep studies using EEG and polysomnograpy.

All right, so then last week I went on my annual ski trip to Lake Tahoe.  By history, I know that I sleep less well during travel and high altitude can influence sleep causing difficulty with onset insomnia and less deep sleep.  So I took the Sleep Cycle app along to Lake Tahoe and the figure at the left shows one of my night sleep plots.  I awoke in the morning with the alarm feeling like I had not slept well and that I had not had much good quality deep sleep.  The plot shows this to be the case.  I had 3 or 4 periods of being awake during the night.  One period of being awake around 430 am appeared to last at least 30 minutes.  There is less deep sleep and my total sleep time is less, as I was getting up earlier than my typical morning wake time.  


So this showed that Sleep Cycle was doing a reasonable assessment of my sleep pattern as the time in deep sleep approximated my sense of sleep quality.

So the next step in looking at Sleep Cycle was to see if it could monitor the potential therapeutic effect of taking a medication for sleep.  So after a night of poor sleep, I took a well-known sleep aid and started the Sleep Cycle app hoping for a good night's sleep and the sleep plot data to prove it.


The 27-28 January sleep plot shows the effect of the use of the sleeping pill.  There was a quick transition to a deep sleep that persisted through the first 6 hours of sleep.  After six hours of sleep there were two periods of being awake including one period shortly before the window for the alarm to sound went off.  


The sleep plot was consistent with what my subjective experience felt like.  I felt like I had slept well and in the morning I felt like I had a good night of sleep.  So the Sleep Cycle app confirmed my impression of the night.


Professional sleep study centers commonly use a technique called actigraphy.  Actigraphy typically involves wearing a motion sensing wrist watch like device.  It monitors activity through the night and estimates sleep based on the motion---very similar in principle to the Sleep Cycle app.  The Sleep Cycle app requires you to place your iPhone or i Pod Touch near your pillow.  I knocked if off the bed one night but other nights it was not a problem and seemed to do a good job monitoring sleep.


So I see the Sleep Cycle as the first iteration in the development of low-cost good quality actigraphy.  It seems to have excellent clinical potential.  For example, physicians might like to see 2 or 3 nights of Sleep Cycle data in the assessment of insomnia complaints.  They might also like to use it for monitoring response to treatment.  I certainly enjoyed this app and plan to continue to use it.  


Disclosure:  I have no financial interest in the Sleep Cycle app and have not been paid to write this review.