01/02/2016 6:45 AM AEDT | Updated 15/07/2016 12:51 PM AEST

Smart Alarms Wake You In ‘Dream Sleep' -- Learn How They Work

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Women in white t-shirt lying in a bed and looking at her mobile phone (macro)

A good night’s sleep is one of life’s most desired yet often unobtainable luxuries. Just ask any new parent, shift worker or musician on the road.

Recently, sleep has become sexy, as we have learnt it is linked to better skin, increased productivity and optimal health (as well as just feeling daisy-fresh).

It’s little wonder then that people have started tracking their sleep, in addition to their steps, activity and water intake by using fitness wearables and smartwatches.

Many users swear by the 'Smart Alarm' function -- an alarm that wakes you within a 30 minute window (15 minutes each side of your set wake up time) when you are said to be in a particular cycle of sleep to ensure you feel refreshed rather than groggy.

“The way these devices track sleep is by measuring your movement throughout the night -- this is called actigraphy,” St. Vincent’s Hospital sleep specialist Dr Dev Banerjee told The Huffington Post Australia.

“It works on the premise that if you’re in deep sleep, you’re nice and still. If you’re in light sleep you might do a bit of a shuffle and if you’re awake, you’re obviously more active."

There are four cycles of sleep -- light, deep, dream and wake.

“Biologically we tend to feel most refreshed if we wake out of dream sleep which is associated with rapid eye movement sleep (REM) -- so it’s assumed it is this cycle that a smart alarm will wake you up from,” Banerjee said.

Whereas if you are waking up out of non-dream sleep, or what’s called slow wave sleep (deep Non-REM), which tends to be the earlier part of the night, that’s when you will feel quite groggy.

Each sleep cycle is roughly two hours in duration and you do three to four cycles each night.

Banerjee likens these cycles to that of a manual car in terms of its gears.

“You always start off in first gear (light sleep), then go into second (deep), third (dream) and fourth (wake). If you stop the car and you were in third gear, you wouldn’t restart it in third gear. You’d have to go back into first -- just as you would with sleep -- you’d go back to light sleep,” Banerjee said.

Unlike our canine friends, when humans dream there is very little movement -- and it is at this stage, while dreaming, that our muscles are most relaxed.

“It’s important to note that these devices will most likely adopt a computer algorithm based on the biology of sleep -- which means if you’re in X cycle you’ll be out of it in Y minutes -- this enables the smart alarm to wake you at what it believes to be the correct cycle,” Banerjee said.

This of course may not always be correct as Banerjee explains the only way to accurately measure REM and non-REM sleep is having various sensors attached to your head called EEG leads which measure brain waves.

“These new technologies are a great awareness tool for sleep deprivation in that they make you responsible and responsive for the amount of hours you sleep,” Banerjee said.

“Many busy professionals don’t get the opportunity to sleep for eight hours each night. The advantage is that these devices act as a negative feedback system -- so if your smartwatch has told you that you only had five hours sleep the night before -- you’ll make an effort to get to bed a little earlier,” Banerjee said.