What ‘smart’ watches get wrong and right when tracking the quality of your sleep

Smart watches have become a common accessory in modern life, offering users insights into their health through features like step counting, heart rate monitoring, and, increasingly, sleep tracking. Yet, despite their popularity, these devices often fall short when it comes to accurately assessing the quality of sleep. A growing body of evidence suggests that while wearables can provide useful data, especially for identifying patterns over time, they struggle to capture the nuanced aspects of sleep cycles and stages. In Ireland, where an estimated half of the population uses smart wearables, the reliance on these devices for sleep assessment has sparked debate among researchers and healthcare professionals. These gadgets typically track not just how long someone sleeps, but also the different phases, deep, light, REM, and awake, that make up a complete sleep cycle. However, experts argue that this level of detail is rarely reliable. Dr. Cailbhe Doherty, a researcher and assistant professor at UCD's School of Public Health, explains that while wearables are moderately effective at measuring total sleep duration, they are not clinically useful for determining the exact stages of sleep. Instead, they rely on indirect methods such as heart rate variability and wrist movement to estimate sleep stages, which can lead to inaccuracies. The concept of a "sleep score," often displayed on these devices, has become a point of contention. Users may find themselves anxious about their scores, even when they know the measurements are not always precise. This anxiety can paradoxically affect their ability to sleep well. The issue extends beyond individual concerns; it reflects a broader shift in how society views sleep. As health experts emphasize the importance of quality sleep for overall wellness, the demand for accurate tracking tools has increased. However, the current capabilities of wearables remain limited. Despite these shortcomings, there is optimism about the potential of wearable technology to improve sleep habits. Dr. Doherty acknowledges that while the specific numbers may not be reliable, the consistent, moderate inaccuracies can still offer valuable insights. By monitoring trends over extended periods, users may identify changes in their sleep patterns that warrant further attention. Moreover, the continuous improvement of algorithms suggests that future iterations of these devices could offer more accurate assessments. Sleep scientists, however, caution against placing too much trust in these devices. Polysomnography, the gold standard for sleep measurement, involves attaching electrodes to the scalp and other parts of the body to monitor brain waves, eye movements, muscle tone, and other physiological indicators. This comprehensive approach allows for a detailed analysis of sleep stages, something that wearable devices cannot replicate. According to Prof. Andrew Coogan, a behavioural neuroscientist at Maynooth University, the idea that a simple wristband could replace such sophisticated equipment is somewhat unrealistic. Nevertheless, the widespread adoption of wearables has contributed to greater awareness of sleep hygiene. Many users report adopting healthier bedtime routines and making lifestyle adjustments based on the feedback they receive. While these devices may not revolutionize the field of sleep science, they have played a role in educating the public about the importance of restful sleep. As the technology continues to evolve, the challenge lies in balancing user expectations with scientific reality. With millions of people relying on these tools, there is a clear market incentive for manufacturers to enhance accuracy. Companies like Oura Ring have already made strides in improving sleep tracking, suggesting that progress is possible. Nonetheless, the journey toward truly reliable sleep monitoring remains ongoing.