Modern wearables have long since ceased to be just pedometers, becoming full-fledged tools for interacting with the digital environment. Xiaomi Band 4 NFC became the first fitness tracker company to receive a built-in module of short-range contactless communication, which radically changed the user experience. Many owners are wondering about the mechanics of the process and security of data transmission, especially given the limited size of the device.
Unlike smartphones, where the antenna takes up a significant amount of space, the tracker uses a miniature chip integrated directly into the body. NFC (Near Field Communication) in this model operates at 13.56 MHz, providing communication at a distance of up to 10 centimeters, which allows you to use the bracelet to pay for fares, unlock doors and authorization in smart home systems without having to reach the phone.
The module activation occurs automatically when the device is brought to the reader, if the Mi Fit (or Zepp Life) application selects the default card. The energy consumption of the technology in standby mode is almost zero, since the chip enters active mode only when there is an electromagnetic field from the terminal, which is why the autonomy of the bracelet is practically not affected by the presence of this feature.
⚠️ Attention: Module NFC Band 4 only works in Card Emulation mode, which means you can't use the bracelet to scan tags or transfer files from other devices, just for reading terminals.
Technical features of the chip and antenna
The engineering solution used in the fourth bracelet model is based on the use of a specialized controller that takes over the processing of security signals. The antenna is designed as a spiral winding located around the perimeter of the tracker, which provides a stable signal even when tightly attached to the wrist. Inductive communication allows you to transmit encrypted data packets in fractions of a second.
It is important to understand that NFC-The chip in this device is not a full-fledged analogue of bank cards with dynamic encryption (tokenization), as in Apple Pay or Google Pay. It uses a method of static emulation, where the bracelet simply transmits to the terminal a unique card ID recorded in its memory. This imposes certain restrictions on the types of cards and banking systems supported.
Why don’t all cards work with a bracelet?
Standard encryption is used to ensure data security during transmission, however, critical information such as pin codes is not stored on the tracker itself.The card ID that reads the terminal is a virtual copy associated with your payment system account. In the event of a loss of the device, you can always delete the card remotely through the application.
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The technology in Band 4 uses static emulation, making it ideal for access cards and transport cards, but restricts use with bank cards without tokenization support.
Configuring and activating the communication module
The initial configuration process requires a smartphone with Android or iOS operating system and the Mi Fit application installed. After pairing the bracelet, you need to go to the device profile and find the section responsible for setting the profile or map, and this is where the virtual key is associated with the physical tracker.
The global version uses Mi Pay support (in limited regions) or emulation of transport maps of major cities, and activation takes several steps: choosing the type of card, entering data and final writing of keys to the memory of the bracelet, the entire process takes no more than two minutes with a stable Internet connection.
1. Update the bracelet firmware to the latest version
2. Open the Mi Fit app and go to profile
3. Select "NFC" or "Map"
4.Click "Add card" and follow the instructions on the screen
5. Wait for the data recorder to be completed-->
It's worth noting that some features, like Alipay, require pre-authorization in the service, you create a special payment code that is downloaded to the device, and then you just have to hold your wrist to the seller's scanner to make a purchase, even if the phone is far away or discharged.
Use of transport maps and access cards
One of the most popular features is the emulation of transport cards. In China, where the technology is developed as widely as possible, the bracelet supports dozens of city maps. For users from other countries, the ability to add access cards through the Access Card function allows you to replace a bunch of physical keys with one gadget on your hand.
To copy an access card, you need to hold the original key (card or fob) to the back of the bracelet at the time of reading, the system considers a unique UID (identifier) and writes it to its module. However, it is worth considering that modern access control systems (ACS) often use data encryption in memory sectors, not just UID, which makes simple copying impossible without special equipment.
| Type of card | Frequency | Support for Band 4 NFC | Limitations |
|---|---|---|---|
| Transport (China) | 13.56 MHz | Complete. | It only works in the regions of China. |
| Doorway (UID) | 13.56 MHz | Partial | Does not copy encrypted sectors |
| Banking (Visa/MC) | 13.56 MHz | No (no tokenization) | Requires Mi Pay support |
| Staff member (Pass) | 13.56 MHz | Depends on the ACS | An administrator may need to register. |
If your access card has a complex level of protection, simply copying through the wristband menu may not work. ID-Your bracelet's code is in the database of the intercom or the turnstile manually, equating it with a regular access card. UID bracelet in the application or through special commands.
⚠️ Warning: Do not try to copy cards with a frequency of 125 kHz (old intercoms, key fobs "digit"). NFC It does not physically support this standard and only operates at 13.56 MHz.
Payment through Alipay and Mi Pay
The payment function in Band 4 is implemented through integration with popular payment systems. In global versions of firmware, the main partner is Alipay. NFC-Painting: The bracelet generates a dynamic QR-code NFC-signal for authorization of debiting funds from the tied account.
When paying via NFC, the terminal reads the token that is transferred to the processing center for verification. The security of the transaction is ensured by the fact that real card data is not transmitted directly. However, as mentioned earlier, direct payment by bank cards (Visa, MasterCard, Mir) through an integrated module without intermediaries in the form of Alipay or Mi Pay in this model is not supported due to the lack of a certified Secure Element chip for the banking level.
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For quick payment via Alipay, make sure that the application has funds on its balance, as the bracelet is offline and cannot request confirmation from the phone at the time of purchase.
The payment process takes seconds. You just need to wake up the bracelet screen (by lifting your wrist or pressing a button) and bring it to the terminal. Vibration and audible signal (if enabled) will confirm successful data transfer. Cost statistics can always be viewed in the history of transactions within the partner application.
Compatibility issues and regional constraints
One of the main difficulties in using NFC-The functions are regionally linked. Chinese version of the bracelet (CN Version has advanced local services functionality that is often not available in the Global Version.When you change the region in the application or flash the device functionality of the module can be limited or completely blocked by the manufacturer.
There are also problems with compatibility with operating systems. NFC In conjunction with third-party devices, Apple’s policies are severely limited, and iPhone users may face the inability to record cards or use some of the payment features that are available to Android smartphone owners. Data exchange protocols between iOS and tracker do not always allow you to fully manage the data NFC-module.
Often, users are faced with a situation where the bracelet stops seeing cards after a software update, this is due to changes in security algorithms or bugs in a new version of the firmware, in which case a complete reset of the device and re-binding, or rollback to the previous version of the software, if technically possible.
Can I unlock the full functionality of NFC?
Impact of NFC on Autonomy and Performance
Many potential buyers fear that constant signal search or active use of NFC will quickly land the battery. Practice shows that the module’s impact on the overall power consumption of the Xiaomi Band 4 is minimal.
The reduction in operating time can only be observed with very heavy use, for example, if you use the bracelet to pass through turnstiles dozens of times a day. In normal scenarios (2-3 pay or pass per day), the difference in autonomy compared to the version without NFC is almost not noticeable and is less than 1-2 days on a full charge cycle.
The performance of the tracker itself is not affected either. The operating system of the bracelet is optimized to work with background processes, so activation of NFC does not cause "hangs" of the interface or delays in displaying notifications. Code optimization allows you to process requests prioritized without blocking other functions of the device.