A recent report from FMI (Future Market Insights) estimates that the global sleep tracker market hit $1.8 billion in 2021. This is expected to grow to $3.1 billion by 2028. This comes as no surprise. According to the Sleep Foundation, in the U.S. alone, 30-48 percent of adults were said to be suffering from insomnia in 2021. Wearable tech is only one element in a sleep industry. According to BCC research, the global market for sleep aids is set to grow to $112.7 billion by 2025, from 2020’s $81.2 billion, with a compound annual growth rate (CAGR) of 6.8% for the period of 2020-2025.

The issue with sleep

There are varying estimates and projections but it all boils down to one fact – many people across the world struggle to get a good night’s sleep. The rising prevalence of sleep disorders such as insomnia, sleep apnea and circadian rhythm sleep disorders has increased the demand for sleep tracking. A few weeks ago, I decided to check how four major smartwatch brands track sleep. This involved sleeping with four wearables strapped on to my wrist and, thankfully, that didn’t affect the quality of my sleep. Most experts will tell you that three things matter: when you sleep, how you sleep (your sleep quality) and how long you sleep (7 hours is usually the magic number). Most smartwatches keep tabs on these sleep variables.

Wearable sleep tech

Accelerometers: Small motion sensors in your wearable that measure how much movement you’re making while you sleep. This data is analysed with an algorithm to estimate sleep time and quality.

Heart rate monitors: It monitors sleep stages from REM (Rapid eye movement) to deep and light sleep by keeping a tab on heart rate.

Microphones: Some smartwatches use microphones that help measure your respiration by tracking snoring, sleep apnea, and how frequently you wake up during the night.

The stages of sleep

Many smartwatches break down your sleep scores or patterns into stages. Garmin defines these as:

Light Sleep: Eye movements and muscle activity begin to slow down as the body prepares for deep sleep.

Deep Sleep: Also referred to as restoration mode, where the body will recover, building bone and muscle, and boosting your immune system Eye and muscle movements stop completely. Heart rate and breathing slow down.

REM Sleep: Also referred to as the dream stage. The brain is almost as active as when you are awake. REM sleep is important for forming memories and processing information.

How smartwatches track sleep

Fitbit: I’ve used Fitbits over the years, and, for this comparison, it’s the Fitbit Sense I’ve put to the test. Fitbit’s personalised sleep score (0 to 100) uses heart rate and restlessness among other factors, while their heart rate sensors and motion detectors work behind the scene. The Sense tracked sleep stages and also times when I was awake in bed. Fitbit’s trackers allow you set sleep schedules and sleep goals. The Fitbit Premium (Rs 999/year) gives you a detailed Sleep Score breakdown as well as Snore and Noise detect. You also get guided sleep sessions.

Garmin: Many of the brand’s smartwatches are kitted with an optical heart rate sensor. Garmin also uses Pulse ox (to measure saturation of oxygen in the bloodstream; also referred to as SpO2 tracking), and respiration tracking (breaths per minute). I tried the sleep tracking on the Garmin Epix. The Advanced Sleep Monitoring (ASM) leans on the optical heart rate sensor that measures heart rate and Heart Rate Variability (the time measured between each heartbeat) combined with the accelerometer, to determine when you fall asleep, when you wake up, and what level of sleep you are in.

Apple Watch: I used the Apple Watch 7 that offers 33 percent faster charging compared to its predecessor thanks to a new charging architecture and Magnetic Fast charger USB-C cable. Many users now feel more confident to strap on their Apple Watch when they hit the bed, knowing that they can fast charge their watch. Apple’s sleep tracking focuses more on sleep quantity than quality – you don’t get breakdowns of sleep stages and there are no sleep scores. Aside from sleep times, you also get heart rate and calorie burn stats. What we like about the Apple approach is the schedule and bedtime routine you can set that helps you meet your goals.

Samsung: I used the Samsung Galaxy Watch 4 with its new BioActive Sensor. The Watch 4 uses advanced insights from the National Sleep Foundation. Samsung also offers a sleep score, while the latest software update also offers a sleep coaching program. The Watch 4 tracks multiple variables including sleep duration (and actual sleep time), sleep stages, blood oxygen levels, sleep consistency and snoring data.