Overview
Earlier this month, Xiaomi released a new Mi Band. Although it arrives 15 months after the first-generation Mi Band, the Light-Sensing edition is not a full new generation; its main change is the addition of heart-rate monitoring, so it is effectively a half-iteration. Shortly after launch we received a unit and tested it for several days. Visually it differs little from the standard edition.
Size and Design
Because a photoplethysmography (PPG) optical heart-rate sensor was added, the Light-Sensing edition has slightly different size and weight:
· Length: 37 mm (standard edition 36 mm)
· Width: 13.6 mm (standard edition 14 mm)
· Thickness: 9.9 mm (standard edition 9 mm)
· Weight: 5.5 g (standard edition 5.0 g)
Overall, the appearance is similar to the standard Mi Band: a long cylindrical body with a sandblasted aluminum shell and polished chamfer around the body. The middle of the module still has three indicator lights made by laser drilling; they provide sufficient light transmission and do not affect the band’s IP67 water resistance.
Strap and Wearability
The review unit came with a black rubber strap. Without external help, putting the band on or taking it off can feel a little awkward. Because my wrist is not large, fastening it on the tightest notch was comfortable: the band itself is light at 5.5 g, and the rubber strap conforms closely to the wrist. The charging method is the same as the standard edition: the module must be pried out of the strap and connected to a dedicated charger. Reinstalling the module is not easy; the strap must be removed and stretched to push the module back in. Note that the Light-Sensing edition’s charger is not compatible with the standard edition’s charger.
Features
After installing the companion app on an iPhone or Android phone and signing in with a Xiaomi account, entering personal details such as height and weight, and binding the band, the following features are available:
· Activity tracking: step count and graphical display of activity throughout the day
· Sleep tracking: automatic sleep recording
· Smart alarm: vibration intensity adjusted based on sleep depth
· Incoming call reminder: vibration and blue light flash if a call is not answered within 20 seconds
· Band ID: when wearing the band, the phone can be unlocked without a password, functioning as an authentication device
These functions operate similarly to the standard edition. See our previous review of the standard Mi Band for more detail. The remainder of this review focuses on the Light-Sensing edition’s heart-rate monitoring.
Heart-Rate Measurement Method
The Mi Band Light-Sensing edition uses photoplethysmography (PPG). Most devices that provide heart-rate monitoring, including some smartwatches and fitness trackers, use PPG. PPG works by using LEDs together with a photodiode to illuminate blood vessels for a period and measure changes in green-light absorption by the blood to derive heart rate. With PPG devices, users should avoid external light interference and ensure the sensor on the back of the band makes firm contact with skin, especially during heart-rate measurement.
Real-Time and Static Monitoring
The band supports real-time heart-rate monitoring, so in theory a runner could view their current heart rate while running. However, because the band has no display, continuously monitoring heart rate requires watching the phone screen while running, which is unsafe and inconvenient. After a run, the exercise summary only shows the average heart rate for the activity, not the heart-rate trend over time. These limitations reduce the practical usefulness of real-time monitoring.
The band can also perform static heart-rate measurements. For a single static measurement, users should raise the forearm to chest height and keep the band still during the measurement.
Accuracy
Accuracy is a common concern. In multiple comparisons with an Apple Watch, the Mi Band’s results were nearly identical. In most tests the readings matched exactly; on a few occasions they differed by 1 to 2 bpm, which is negligible for consumer wearable usage.
Battery Life Trade-Off
The Light-Sensing edition’s key trade-off is battery life. The standard Mi Band has a theoretical 30-day battery life, while the Light-Sensing edition with real-time heart-rate monitoring has a theoretical 10-day battery life. In real use beyond one week the band can struggle to maintain charge, reflecting the trade-off between added functionality and battery longevity.
Price and Payment Integration
The Light-Sensing edition is priced at 99 yuan. Its main advantage is offering heart-rate monitoring at that price point, which is notable in the current market. The Mi Band’s identity-as-authentication capability is expanding to more services; some mobile payment services, such as Alipay, already support using the Mi Band instead of a payment password.
