last updated 15 Apr 2020
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Contents: Reviews | About Sleep | Pillow vs Sleep Cycle:

Note: Apple does not have their own sleep app.
 Apple is rumored to be releasing their own sleep app
 in a new release of watchOS at the end of 2020.

There are 2 types:
1. Detect sleep thru sound an motion sensing with your phone on the bed.
2. Use an apple watch

1. Without watch:

The Best Sleep-Tracking App for 2020 | Reviews by Wirecutter
As a health journalist, I've followed the scientific research on sleep
 for more than a decade. For this guide, I interviewed product specialists
  and brand executives in the sleep-tracking field, sleep doctors 

SleepScore 4.3 (4.6K)  premium $49/yr
It's more intuitive and provides deeper sleep analysis
 and advice than other apps.
more transparent about the science behind its app.

Tom's Guide

Sleep Cycle 4.7 (175K) $26/yr American Sleep Association
Tom's Guide
Uses sleep cycle theory to wake you at just the right time,
 ensurin you're getting optimal rest. 
Simpler interface, less data.
A good choice for people who simply want to see sleep patterns
 and how they correlate with diet and exercise.

2. Apple Watch The best sleep tracking apps to download for your Apple Watch | Wearable AutoSleep Track 4.7 (27K) $2.99 When put up against a dedicated sleep tracker, it produced close results, but you can tweak the sensitivity for better accuracy. Sleep++ 4.2 (4.8K) Pillow Automatic Sleep Tracker 4.4 (42K) Best For Figuring Out Why You Can't Sleep WomensHealth Sleepzy 4.2 (9.6K) Sleep Watch 4.7 (178K) Best Sleep Apps For Apple Watch To Try in 2019 | TechWiser Pillow Automatic Sleep Tracker 4.4 (42K) Sleep Watch 4.6 (89K) Sleep++ 4.3 (4K)

Types of Sleep:
  • Light Sleep - You drift in and out of sleep. Your eyes move slowly, your muscle activity is slow, and you would be easy to wake up.
  • Eye movements and brain waves slow down, your body temperature drops, and your heart rate slows down.
  • Deep Sleep - Extremely slow brain waves called delta waves are intermixed with smaller, faster brain waves.
  • You stay in deep sleep and your brain almost exclusively produces the slow delta waves.
  • REM Sleep - Now your eyes are closed but move rapidly from side-to-side, due to the intense dream and brain activity you go through in this stage.
  • Sleep Quality:

    Americans spend an average of 7 hours and 18 minutes in bed each night. They go to bed at 11:39 p.m., wake up at 7:09 a.m., spend 23.95 minutes snoring, have an average sleep quality of 74.2 percent, and rate their wake-up mood at 57 on a scale of 100. Feb., 2019
    Source: What we know about America’s healthiest, happiest and best-rested people - Sleep Cycle
    See Sleep Quality under health.

    optimal values for sleep each stage are 5% Awake, 25% REM, 35% deep, and 35% percent light sleep.
    Source: How does pillow calculate sleep quality? – Pillow

    Pillow vs Sleep Cycle:
    How does pillow calculate sleep quality? | Pillow Pillow takes into account body motions during sleep, as registered by the device's accelerometer and gyroscope, and also the noise level as recorded by the device's microphone. These data are processed by a scientifically backed algorithm in order to calculate your sleep quality index.

    Sleep quality ranges from 25% - bad to 90% - great

    Generally accepted optimal values for sleep each stage are 5% Awake, 25% REM, 35% deep, and 35% percent light sleep for an adult,

    Sleep Cycle:

    It uses a patented technology.

    Review of Sleep Cycle App for Timing Awakenings | VeryWellHealth
    Some of their comments:
    There are many graphs, tracking sleep quality, Heart rate, Sleep time, all the way up to sleep quality affected by the moon.
    Some Issues:
    If you have a soft mattress pad or other bedding, the accuracy will suffer even more because movements will be missed.

    It's called Sleep Cycle Alarm Clock because it has a feature where you set the time you want to wake-up and 30 minutes before that it monitors signals from your body to wake you softly when you are in the lightest possible sleep stage. My and others experience was that it woke us too soon.