Background
On September 9, 2014, at the iPhone 6 launch event, Apple announced the Apple Watch. The device uses a sapphire-covered screen and supports phone calls, Siri voice input, messaging, and similar functions. In addition to those features, the Apple Watch also performs health and activity monitoring, functions commonly found on market smart bands.
Smart bands
A smart band is a wearable device popular with people who are losing weight or who exercise regularly. Smart bands record real-time data about daily exercise, sleep, and diet, and synchronize this data with companion smartphone apps. The collected data is intended to guide healthier habits, and for people with certain medical conditions a smart band can help them monitor their status and, in some cases, transmit information to medical professionals.
Although some smartwatches include more hardware and features, the core health-monitoring functions are broadly similar across the Apple Watch and other smart bands.
How smart bands measure health data
The monitoring capabilities are implemented through sensors such as accelerometers, gyroscopes, a compass, and a variety of physiological sensors. These components can monitor body signals and help generate diet and exercise plans. Given the small size of a wrist-worn band, it is notable that no blood draw or adhesive electrodes are required; the device relies on noninvasive sensing techniques.
Mr. Zhao, a representative of a smart band manufacturer, explained that modern smart bands include a variety of sensors. Many smartphones also include sensors such as a basic accelerometer, proximity sensor, and barometer. Smart bands typically add dedicated sensors for heart rate, blood oxygen, and skin temperature. These sensors collect data without harming the body. For measurements such as blood pressure and heart rate, the device infers values from changes in skin blood distribution.
Apple Watch heart-rate monitoring uses a sensor located on the back of the watch beneath a protective sapphire surface. The sensor employs infrared light and visible LEDs together with a photodetector to detect the user's heart rate.
For activity monitoring, accelerometers, gyroscopes, a compass, and pressure sensors detect arm vibrations and swing amplitude to infer the wearer’s activity.
Activity monitoring technology is relatively mature compared with some health measurements. Current solutions can estimate calories burned from inputs such as body weight, activity duration, and speed. Smart bands also record sleep by detecting micro-movements during rest and analyzing those signals to infer sleep stages.
Collecting sensor data is only the first step. Mr. Zhao noted that after the band gathers the various physiological and motion data, the final results are produced by the companion smartphone software. For example, the Apple Watch includes around ten sensors; the sensor data is forwarded to Apple's HealthKit or to compatible third-party apps, which analyze the data and provide recommendations to users.
Essential features: health tracking and activity monitoring
There is demand for a persistent personal health monitor that performs routine checks and alerts the user to concerning trends or events. Smart bands are an attempt to address that demand. Patients with hypertension or diabetes want to monitor their conditions; people trying to lose weight or suffering insomnia want tools that can support behavior change and provide evidence-based suggestions.
Given current technology, wearable devices are among the few practical options for continuous, passive monitoring. Carrying a glucometer while shopping or a scale in a bag is impractical; a compact wristband can collect relevant signals while minimizing the influence of most environmental factors. This practicality is a primary reason wearables were developed.
Mr. Zhao added that as smart bands have developed, many functions have been integrated into them. Health tracking and activity monitoring have become defining features. Although aspects such as precise sleep staging are still debated, overall utility is generally acceptable. He also noted that wearing an attractive band can improve some users’ mood.
That said, remembering the device cost may reduce that positive feeling for some users.
Daily life and limitations
No device or technology is without drawbacks. Users have reported issues such as certain bands failing to charge; investigations sometimes trace those issues to design flaws. Sleep staging remains contentious: deep sleep is typically inferred from reduced body movement and lowered sensory responsiveness, and current wrist-worn devices still have difficulty providing highly accurate sleep-depth measurements. These are technical challenges that wearable designers must address.
Two practical inconveniences stand out. First, many smart bands are expected to be worn continuously, including during sleep and often during showering, otherwise their functions are compromised. Some users object to the practical burden of continuous wear.
Second, bands plus companion apps often prescribe activity and diet plans based on monitored data. Purchasing and using the product tends to imply that users should adapt their lifestyle to the device’s recommendations. That dynamic moves the relationship between user and device into a behavioral or even philosophical domain: the band issues guidance, but whether those recommendations are followed depends entirely on the user’s discipline.
With current technology these two issues are not fully resolved. Whether future designs will find better solutions remains to be seen. A straightforward way to avoid these constraints is simply not to buy a smart band.
Future of smart bands
Smartphone functionality has evolved from simple communication to roles such as personal information manager. The emergence of smart bands and other wearables suggests another role shift, where devices provide real-time physiological monitoring, health recommendations, and care planning. These capabilities extend the functions of smartphones. In the future, phone and band functionality may converge, as some smartwatches already demonstrate.
For healthcare, the development goal for wearables is to replace older, less efficient monitoring methods wherever possible. We already have wrist blood-pressure monitors; smartwatches add more monitoring methods. Once wearable sensors achieve sufficient accuracy and timeliness, additional functions will likely be layered on top. For example, an automated alert might say, "Owner, you are expected to experience gastrointestinal distress in approximately 30 minutes; please avoid going out."
