There are so many tracking devices for sleep out there. What do they do?

Activity trackersThere are many different devices now available for measuring sleep. Two years ago, smartphone apps leaving your phone under the pillow were all the rage. Now activity trackers, generally worn on the wrist are used, and will be more accurate with new models that incorporate heart rate measurement. Wireless devices that can measure sleep from the bedside table are becoming available, as are devices that can be fitted to the bed itself.

Movements during sleep – the key to activity trackers measuring sleep

Whether awake or asleep you are always moving. But, movements whilst awake follow different patterns compared to movements during sleep. During wakefulness, movements are generally bigger and don’t occur regularly or predictably. But, during sleep, movements are smaller and at times can follow a predictable pattern. Movements also differ between different sleep stages, with there generally being less movement in deeper non-REM and REM sleep. These differences between movements during wake and sleep can be used to measure sleep and get an idea about what type of sleep you are having.

Smartphone apps

Sleep cycle app

Sleep cycle app

There are a number of apps that work by placing your smartphone under your pillow while you sleep. Sensors in the phone track movement and equate any movement they sense to either being awake (a lot of movement) or light sleep (slight movements). Whilst the concept underpinning these apps is sound, having your smartphone under your pillow is not the best way of tracking movement during sleep, so they aren’t particularly accurate. The most well known of these apps is the Sleep Cycle app. A reporter from the Daily Mail (UK) used it for a week and wrote about the results.

Wrist-based activity trackers

Jawbone UP3

Jawbone UP3

Because the ability of a smartphone to detect movement when placed under a pillow or sheet is limited, the next phase in monitoring sleep, was with wrist-based activity trackers. Whilst these are mainly used to measure steps or activity whilst awake, to track exercise, they can also be used to track movement during sleep and therefore measure sleep. This way of measuring sleep has been used in medical research for many years and is called actigraphy. One of the advantages of this actigraphy has been that people can wear devices for long periods of time, weeks or months, which allows patterns in their sleep over time to be measured.Using the prinicples of actigraphy, there is now a large range of wrist-based activity trackers available. Some of the best known devices are Fit Bit, Garmin’s range of devices and Jawbone devices.  Actigraphy still has it’s limitations as it uses movement to try to determine wake vs sleep and during sleep different sleep stages. However, if heart rate is added, the combination of patterns of movement and variations in heart rate, can measure sleep, particularly sleep stages, much more accurately. So, newer versions of these devices that are just being released, such as the Jawbone UP3, can measure sleep and stages of sleep more accurately.

The Apple watch has the ability to measure movement and heart rate. However, as it needs to be taken off and charged at night, there hasn’t really been a focus on it’s potential as a sleep tracking device. It will be interesting to see if the Apple watch’s ability to measure sleep is utilised more in the future as battery life gets better.

Bedside wireless monitoring devices

ResMed S+

ResMed S+

Another type of sleep monitoring device that is only just becoming available, are devices designed to be placed on the bedside table that monitor sleep wirelessly. The only product that’s currently available, and only in the US, is the ResMed S+. It uses ultrasound technology to measure movement not just of the body, but also of the chest wall to detect breathing patterns and heart rate. Using this combination of measurements it generates a sleep quality score that is fed back to your smartphone and gives you pointers on aspects of sleep that could be improved. This is the sort of thing I could see people with obstructive sleep apnea having by their bedside to monitor control of sleep apnea, whether that be with CPAP or other devices such as mandibular advancement splints.

Devices fitted to your bed

Beddit

Beddit

A really interesting device is Beddit. It is a sleep monitor that you lay on whilst sleeping. It accurately measures heart rate and breathing and via those signals is able to measure sleep. This data is fed back to your smartphone and gives a sleep quality score. You can even use their app to get data from a number of Beddit devices, so you can keep an eye on the sleep of everyone in your house, every night. There is good research behind the Beddit technology, and whilst it’s not yet widely available (but can be ordered online), as this technology advances we may well find our mattresses fitted with sensors that measure our sleep.

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