Sleep trackers track our sleep by measuring our movements and heart rate, both of which correspond to our sleeping pattern.
Unlike early trackers, which simply monitored movement, modern trackers use much more sophisticated technology.
Data based solely on our movement was frequently unreliable because, of course, a person could be lying still but very much awake, Will Turner, co-founder of team-focused fitness app GoJoe, explains.
However, new technologies have emerged that, when combined with movement data, make this tracking more reliable.
The most common method is photoplethysmography (or PPG), in which the blood beneath the skin reflects the red light emitted by your smart watch while absorbing the green light.
Each heartbeat allows for more green light absorption, and in between heartbeats, less green light can be absorbed, allowing your device to track your heart rate alongside your movement data and determine when you’ve been sleeping.”
Some devices also employ ‘pulse oximetry,’ which measures the level of oxygen saturation in your blood.”
This feature, which is generally regarded as more reliable than the ‘red light, green light’ method, employs a combination of red and infrared sensors that respond differently to oxygenated or deoxygenated blood.
Highly oxygenated blood absorbs more infrared light and reflects less red light back, allowing your device to analyze your sleep.
Can sleep trackers improve sleep?
The jury is still out on this, not just because everyone’s sleep patterns differ, but also because many experts believe that tracking sleep may be doing more harm than good for certain people.
There’s even a medical term: orthosomnia. Orthosomnia is a condition in which people obsess over the results of their sleep and fitness trackers. Unfortunately, unlike eating five pieces of fruits and vegetables or exercising every day, you typically have no control over whether or not you sleep for eight hours. And if people put pressure on themselves to sleep better, the chances are they won’t.